Module 1. History, status and scope of cheese industry

Lesson 1HISTORICAL DEVELOPMENTS IN CHEESE MANUFACTURE AND WORLD MARKETFOR CHEESE1.1 History and Developments in Cheese ManufacturingCheese is one of the oldest foods of mankind. It is commonly believed that cheese evolved in theFertile Crescent between the rivers Tigris and Euphrates in Iraq some 8000 years ago. The socalled Agricultural Revolution occurred here with the domestication of plants and animals.It seems that cheese originated accidentally as a result of the activities of nomadic tribes. Sinceanimal skin bags were a convenient way of storing liquids for nomadic people, these were usedfor storing surplus milk. Fermentation of the milk sugars in the warm climate prevailing wouldcause the milk to curdle in the bags. The swaying animals would have broken up the acid curdduring journeys to produce curds and whey. The whey provided a refreshing drink on hotjourneys, while the curds, preserved by the acid of fermentation and a handful of salt, became asource of high protein food supplementing the meagre meat supply.This activity gave rise to the assumption that cheese was evolved from fermented milks. It isperhaps more probable that the crude fermentations progressed in two ways: (1) production ofliquid fermented milk such as dahi, yoghurt, laban, kumiss and kefir and (2) drainage of wheythrough a cloth or perforated bowls, to leave solid curds which when salted, became cheese.Cheese was a prominent item of the Greek and Roman diet as much as 2500 years ago. It isreferred to in the Old Testament several times. Cheese making has been an Art handed down fromgeneration to generation, and evolved as a gourmet food over the years.Until the 18th century, cheese making was essentially a farmhouse industry, but towards the e ndof the century scientific findings began to provide guidelines, which were to have an impact onthe process of making and ripening cheese. Thus, cheese making became an Art with Science.The process has undergone many developments during the course of its history.Now-a-days, instead of using the enzyme rennin, a synthetic chymotrypsin derivative issometimes used, along with extracts from molds and plants. The plethora of flavors is due to themanipulation of a variety of factors including the kind of milk used (cow, sheep, goat, buffalo,reindeer, camel, yak, etc.), curdling, cutting, cooking, and forming methods, the type of bacteria ormold used in ripening, the amount of salt/other seasonings added, the ripening and curingconditions (temperature, humidity, time, etc.) and many more.Now the mechanization and automation has been taken to such a high level that several tons ofcheese can be produced without the touch of a hand. Many machines have been developed formass and continuous production of cheese like continuous cheddaring machine, advanced cuttingand cooking vats, pressing machines, stretcher or cooker for some varieties of cheese, etc. All thesewill be discussed in lesson 16.5

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Another development in cheese making is the accelerated ripening of cheese. Traditionally cheeseis kept for ripening for months or even years to develop typical flavour and texture. A great dealof research had been carried out to accelerate the cheese ripening to achieve the desired flavor andtexture in very less time.With over 2000 types, cheese is one of the most versatile foods in the world. Currently, about onethird of the milk produced in the U.S. each year is used in the manufacturing of cheese. Cheesecontains a concentrated amount of almost all of the valuable nutrients found in milk. In 2010, thetop three world cheese producers were: (1) United States of America with 5.10 million tons (2)Germany with 2.08 million tons, and (3) France with 1.90 million tons.Cheese is a protein rich product but at the same time, it also contains a considerable amount of fat.So, the calorie conscious populace of the world reduced the consumption of cheese. Keeping thisin mind, a variety of low fat cheeses have been developed throughout the world to increase itsconsumption and to make it healthier. Now-a-days, work is being carried out to produce low saltcheese as increased salt consumption is leading to increased heart diseases in many countriesparticularly United States.1.2 World Market for CheeseCheese continues to be a popular addition to every day diet, thanks to the high amount of protein,calcium, minerals and vitamins it contains. The consumption of cheese, over the years, hasimproved significantly across the world and subsequently the art of cheese making has nowevolved into a lucrative business.According to a report (Global Industry Analysts, 2010), though the economic recession has put acheck on the cheese consumption pattern across the world, more importantly in the developingnations, the future outlook for global cheese market still remains bright with consumption ofcheese projected to grow by more than 20% during 2008-2015. Purchasing decisions, beingincreasingly guided by price, cheaper yet healthy and wholesome foods are surfacing back intothe spotlight. Consumers are additionally exhibiting shifting preferences from imported cheesebrands to locally produced cheese. Post recession, the demand for organic cheese is slated to makea comeback, with manufacturers expected to expand their product offeri ngs. Innovation andproduct diversification will be the most prominent market strategies for manufacturers andsuppliers in the post recession period. The product mix is poised to change from traditional typesof cheeses to new cheeses that suit the demand in developing dairy markets like China and India.The growing demand for dairy products that meet consumers changing diet and nutritional needswill result into strong growth for innovative and healthier cheese products, such as, lactose -freegoat cheese products, and half-fat and reduced fat cheeses.Europe and the United States lead the global cheese market, by consumption. However, withconsumption levels for cheese in such developed markets nearing saturation, the focus of theglobal cheese industry now shifts towards emerging markets such as Asia-Pacific and LatinAmerica. Cheese consumption in developed economies will be fraught by challenges, such as amatured market profile, limited growth in population, and most importantly the fast agingpopulation, which account for lesser per capita consumption than younger generation. Therefore,any further development in cheese consumption within these markets is likely to be marginal andonly associated with changes in form and type of dairy products consumed. Meanwhile,developing markets such as Asia, Latin America and the combined market of Middle East &Africa, are projected to display superior growth rates over the analysis period (2006-2015). Large

Lesson 2CHEESE PRODUCTION AND CONSUMPTION IN INDIA AND ABROAD2.1 IntroductionThere has been steady increase in the consumption of cheese in most countries worldwide, theannual growth rate in cheese consumption being over 3% with an acceleration expected due toworldwide trend of adopting Western consumption habits with a high level of cheese in the diet.About 40% of total world milk production is converted into cheese. As can be seen from Table 2.1,conversion of milk to cheese has exhibited an increasing trend unlike in case of other products.The major cheese production has centered in Western countries. In 2008, 17.2 million tonnes ofcheese was produced in the world, of which the European Union and United States accounted formore than 50%. Significantly, New Zealand exported 110,000 tonnes (over 75% of the production)and is the worlds number two exporter. Both Australia and Switzerland ranking third and fourth,respectively, exported almost 45% of their total production. All these three countries along withEU accounted for 80% of the total world exports of almost one million tonnes in 1993.Table 2.1 World milk utilization pattern (%)

The scenario of cheese production in India is quite bright because of recent economic reformsbased on globalization and liberalization in the marketing arena that have prompted the Indiandairy industry to penetrate the large international cheese market. The growth pattern of cheeseproduction in India has been quite encouraging, being 800 tonnes in 1977 and 1000 tonnes in 1980.It increased to about 3000 tonnes per annum in 1987. In 1994, the production was estimated at8000 tonnes, against the installed capacity of 9000 tonnes.The growth pattern of cheese production is shown in Table 2.2.Table 2.2 Cheese production in top cheese producing countries (MMT)

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2.2 Mode of Utilization

Cheeses are highly diversified. Names of cheeses number about 2000, although many have littledifferences. The manufacturing procedure and curing through centuries have resulted in theproduction of the cheese which ranges in flavour from extremely mild to very sharp and in texturefrom semi-solid to almost stone hard. Thus cheeses differ in varying degrees in nutritive value,appearance, flavour, texture and cooking properties. Consequently cheese is capable of satisfyinga diverse range of sensory and nutritional demands. The use of cheese is extended by secondaryprocessing methods to create an array of cheese-based products. The major usage levels (per centof total cheese consumed) is: Natural, 39%; Dry, 28%; Processed, 13%; and Low-fat, 20%. The useof cheese as food ingredient accentuated the need for specific and consistent properties, whichmust be attained with correct flavour synergistic with the food. The comparative usage level ofcheese in different food products is shown in Table 2.4. Cheese maker can pro vide a range ofdifferent flavours, texture and compositional properties to suit a variety of needs. It requiresknowledge about its functionalities which can be effectively exploited for the benefits ofconsumers.Table 2.3 Utilization of cheese in different food products

The natural cheese can be eaten as such or on bread, biscuits, etc as slices. At the turn of thiscentury, developments in melting processes, involving natural cheese at various ages, have givenbirth to a line of process cheese products with controlled flavour, texture and extended shelf life.In addition, various shapes, sizes, configurations and sliced versions are created to providevarieties with novel applications. The consumer can use these products as ingredients in cookingof several dishes or as ready-to-eat snacks. These products are designed to be consumed as aspread or as slices in sandwiches and function as dip or toppings on snacks. Cheese crackers arequite popular in Western countries. Natural cheese can be dried to prol ong its shelf life. Driedproducts can be used in bakery products, soups, sauces, snacks, pasta products, ready meals,biscuits, fillings, cheese substitutes/imitations, etc.Cheese consumption opportunities exist around all meals breakfast, lunch, dinner and inbetween meal snacks. We can, therefore, assume consumption of about 20-25 grams cheese perhead twice a week in one form or another. Assuming the Indian population at 100 crores, thisleads to an estimated potential annual demand of about 50000 tonnes. This is the domestic9

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potential in cheese demand. In this projection, the production and consumption of paneer,chhana and shrikhand is not included, though technically they are also classified as cheese.Process cheese spread and slices have proven to be ideal bread-mates. There is a very high growthrate in consumption of bread. Butter, the traditional spread for bread is now avoided by peopledue to its high fat content which is implicated with obesity and cardiovascular diseases. The otherconventional spreads like jam and jelly are avoided owing to their high calorific value. Theintroduction of pizza in India has added new fillip for enhanced consumption of Mozzarellacheese.

Lesson 3DEFINITION AND STANDARDS OF CHEESE3.1 IntroductionThe word cheese is derived from the Old English cese which in turn was derived from the Latincaseus which means correct or perfect thing. Cheese may be defined as the curd of milkseparated from the whey and pressed into a solid mass. This definition of cheese is satisfactorybut too limited and vague from a technical standpoint. Therefore, a relatively complete definitionis as follows:Cheese is the curd or substance formed by the coagulation of milk of certain mammals by rennetor similar enzymes in the presence of lactic acid produced by added or adventitiousmicroorganisms, from which part of the moisture has been removed by cutting, warming andpressing, which has been shaped in mould and then ripened (also unripened) by holding forsometime at suitable temperatures and humidity.The expansion of the numbers of types of cheese makes a simple definition of cheese difficult.Thus the definition, the curd produced from milk by enzyme activity and subsequent separationof whey from the coagulum does not cover whey cheese, lactic cheese, cream cheese and some ofthe cheeses produced by newer techniques, viz. ultrafiltration and reverse osmosis. The definitionis, therefore, not universally acceptable.3.2 Definition of CheeseCheese is the fresh or matured solid or semi-solid product obtained:a) By coagulating milk, skim milk or partly skimmed milk, whey, cream or butter milk or anycombination of these materials, through the action of rennet or other suitable coagulating agentsand by partially draining the whey resulting from such coagulation, orb) By processing techniques involving coagulation of milk and/or materials obtained from milk(provided that the whey protein casein ratio does not exceed that of milk) and which give an endproduct which has similar physical, chemical or organoleptic characteristics as the productdefined under (a).According to the FSSR (2011), cheese means the ripened or unripened soft or semihard, hard andextra hard product, which may be coated with food grade waxes or polyfilm, and in which thewhey protein/casein ratio does not exceed that of milk. Cheese is obtained by coagulating whollyor partly milk and/or products obtained from milk through the action of non-animal rennet orother suitable coagulating agents and by partially draining the whey resulting from suchcoagulation and/or processing techniques involving coagulation of milk and/or productsobtained from milk which give a final product with similar physical, chemical and organoleptic11

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characteristics. The product may contain starter cultures of harmless lactic acid and/or flavorproducing bacteria and cultures of other harmless microorganisms, safe and suitable enzymes andsodium chloride. It may be in the form of blocks, slices, cut, shredded or grated cheese. FSSR(2011) has also defined cheese on the basis of ripening as follows:(i) Ripened cheese is cheese which is not ready for consumption shortly after manufacture butwhich must be held for some time at such temperature and under such other conditions as willresult in necessary biochemical and physical changes characterizing the cheese in question.(ii) Mould ripened cheese is a ripened cheese in which the ripening has been accomplishedprimarily by the development of characteristic mould growth through the interior and/ or on thesurface of the cheese.(iii) Unripened cheese including fresh cheese is cheese which is ready for consumption shortlyafter manufacture.Cheese or varieties of cheeses shall have pleasant taste and flavor free from off flavor andrancidity. It may contain permitted food additives and shall conform to the microbiologicalrequirements prescribed in the regulation.3.3 Classification of CheeseSeveral schemes to classify cheese have been proposed to assist international trade and to providecompositional and nutritional information. The basis for such classification include age, type ofmilk, country of origin, ripening process/agents, important compositional varieties, like moistureand fat, general appearance, texture and rheological qualities. However, none of the aboveschemes is complete in itself. There are about 2000 names of cheeses. It is very difficult to classifythe different cheeses satisfactorily, in groups. There are probably only about 18 types of naturalcheeses. These are: Cheddar, Gouda, Edam, Swiss, Brick, Herve, Camembert, Limburger,Parmesan, Provolone, Romano, Roquefort, Sapsago, Cottage, Neufchatel, Trappist, Cream andWhey cheeses.Such a grouping, though informative, is imperfect and incomplete. These can also be classified onthe basis of their rheology, and according to the manner of ripening as shown below:1) Very hard (grating) - Moisture < 35% on matured cheese and ripened by bacteria, e.g.Parmesan, Romano.2) Hard - Moisture < 40%a) Ripened by bacteria, without eyes: Cheddarb) Ripened by bacteria, with eyes: Swiss3) Semi-hard - Moisture 40-47%a) Ripened principally by bacteria: Brickb) Ripened by bacteria and surface microorganisms: Limburgerc) Ripened principally by blue mould:12

Lesson 4COMPOSITION AND NUTRITIONAL VALUE OF CHEESE4.1 IntroductionCheese is a nutritious and versatile dairy food. It contains a high concentration of essentialnutrients relative to its energy level. Its precise nutritional composition is determined bymultifactorial parameters, including the type of milk used (species, breed, stage of lactation, andfat content) and the manufacturing and ripening procedures. In general, cheese is rich in the fatand casein constituents of milk, which are retained in the curd during manufacture. It c ontainsrelatively small amounts of the water soluble constituents (whey proteins, lactose, and watersoluble vitamins), which partition mainly into the whey. The composition of some varieties ofcheese is given in Table 4.1.Table 4.1 Approximate composition of some varieties of cheese (%)

4.2 ProteinCheese contains a high content of biologically valuable protein. The protein content of cheeseranges from approximately 4-40%, depending upon the variety. It varies inversely with the fatcontent of cheese. During cheese manufacture, most of the whey proteins are lost in whey andthus only casein remains in cheese. Casein is slightly deficient in sulphur-containing amino acids.Thus the biological value of cheese protein is slightly less than that of the total milk protein.Cheese protein is almost 100% digestible, as the ripening phase of cheese manufacture involves aprogressive breakdown of casein, to water-soluble peptides and free amino acids. Hence, asignificant degree of breakdown of cheese protein has occurred before it is consumed andsubjected to the effects of gastrointestinal proteolytic activity. A range of bioactive peptides arereleased during proteolysis of cheese, which exert specific health benefit to the human body (e.g.

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the peptides that inhibit the activity of angiotensin-I converting enzyme which give rise toantihypertensive and immunomodulatory effects).4.3 CarbohydrateThe principal carbohydrate in milk is lactose, most of which is lost in whey during cheesemanufacture. Only trace amount of carbohydrate remains in the cheese, this too is hydrolysed bystarter lactic acid bacteria. Cheese is therefore, a safe food for lactose-intolerant people.4.4 LipidsMost of the cheese varieties are rich in fat. Fat affects cheese firmness, adhesiveness, mouthfeeland flavour and also provides nutrition. It contributes a significant amount of both saturated andtotal fat to the diet. Cheese fat generally contains 66% saturated, 30% monounsaturated and 4%polyunsaturated fatty acids. Thus, cheese represents a significant dietary source of both total fatand saturated fatty acids. The cholesterol content of cheese is a function of its fat content andranges from approximately 10-100 mg/100 g, depending on the variety. Dietary cholesterol hasmuch less influence on blood cholesterol level than dietary saturated fat. Thus, the cholesterolcontent of cheese is of lesser importance than its saturated fat content.4.5 Vitamins and MineralsAs most of the milk fat is retained in cheese curd, the fat soluble vitamins remain in the curd whilemost of the water soluble vitamins are lost in whey. However, some microbial synthesis of Bvitamins may occur in cheese during ripening. In general, most cheeses are good sources ofvitamin A, riboflavin, vitamin B12, and, to a lesser extent, folate. Cheese contains negligibleamounts of vitamin C.Cheese is also an important source of several nutritionally important elements, including calcium,phosphorus, and magnesium. It is a particularly good source of bioavailable calcium, with mosthard cheeses containing approximately 800 mg calcium/100 g cheese. Cheese has a potential rolein supplying extra and highly bioavailable calcium. However, acid-coagulated cheeses (e.g.,Cottage) contain considerably less calcium than rennet-coagulated varieties. Bioavailability of thecalcium from cheese is equivalent to that from milk. It has been reported that 22.9, 26.7 and 25.4%of total calcium was absorbed from cream cheese, whole milk and yoghurt, respectively. Adequatecalcium intake during childhood and in teenage years is important in development of high bonemass which may prevent osteoporosis in the later years.

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Lesson 5PRINCIPLES OF CHEESE MANUFACTURE5.1 IntroductionCheese is the most diverse group of dairy products and is, arguably, the most academicallyinteresting and challenging. While many dairy products, if properly manufactured and stored , arebiologically, biochemically and chemically very stable, cheeses are, in contrast, biologically andbiochemically dynamic, and consequently, inherently unstable. Throughout manufacture andripening, cheese production represents a finely orchestrated series of consecutive and concomitantbiochemical events. These, if synchronized and balanced, lead to products with highly desirableflavors and body and texture, but when imbalanced, result in off-flavors. Considering that thesame raw material (milk) is subjected to a manufacturing protocol whose principles are commonto most cheese varieties, it is fascinating that such a diverse range of products can be produced.No two batches of the same variety and indeed no two cheeses are identical. A further importantfacet of cheese is the range of scientific disciplines involved. Cheese manufacture and ripeninginvolves the chemistry and biochemistry of milk constituents, fractionation and characterization ofcheese constituents, microbiology, enzymology, molecular genetics, flavor chemistry, rheologyand chemical engineering.Cheese consists of a concentration of the constituents of milk, principally fat, casein and insolublesalts, together with water in which small amounts soluble salts, lactose and albumin are found. Toretain these constituents in concentrated form, milk is coagulated either by means of lactic acidproduced by bacteria or by the addition of rennet or by both. A portion of water is removed bycutting, cooking, stirring or draining the curd or by mechanical application of pressure. The cheesemay or may not be ripened; the nature of the process depends upon the particular variety ofcheese.The hundreds of varieties differ very much in size, shape, color, hardness, texture, odour andtaste. However, all cheeses, irrespective of country of origin and method of manufacture possesscertain common characteristic steps as follow:1. They are made from the milk (or derivatives of milk) of certain mammals derivatives2. Souring3. Clotting by rennet or a similar enzyme preparations4. Cutting or breaking up of the coagulum to release the whey5. Consolidation or matting of the curd6. Maturing

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The above traits are common to all cheeses, but the conditions vary considerably. The chief factorsresponsible for differences in the final cheese are:1. type of milk used2. degree of souring and type of souring organisms added3. temperature of renneting and subsequent cooking or scalding of the curd in the whey4. milling and salting of the curd before putting in the hoop or mould5. pressure applied to the green cheese6. time, temperature and relative humidity of ripening7. special treatments such as stabbing the cheese, bathing in the brine and surface treatment toproduce a certain type of coat.5.2 Outlines of Cheese ManufactureCheese manufacture involves the controlled syneresis of the rennet milk coagulum, the expulsionof moisture being affected by: i) acid development, the pH falling from 6.6 to about 5.0 as a resultof lactic acid bacteria of the starter, chiefly Lactococcus lactis subsp.lactis and Lactococcuslactis subsp. cremoris, ii) warmth, the temperature being raised to about 31C for renneting and toabout 38C for scalding the curd, and especially iii) repeated cutting of the curd and stirring.Although some soft cheese varieties are consumed fresh, i.e. without a ripening period, theproduction of the vast majority of cheese varieties can be subdivided into two well -definedphases, manufacture and ripening.

The manufacturing phase might be defined as those operations performed during the first 24 h,although some of these operations, e.g. salting and dehydration, may continue over a longerperiod. Although the manufacturing protocol for individual varieties differ in detail , the basicsteps are common to most varieties. These are acidification, coagulation, dehydration (cutting thecoagulum, cooking, stirring, pressing salting and other operations that promote gel syneresis),shaping (moulding and pressing), and salting. During the dehydration process of cheesemanufacture, the fat and casein in milk are concentrated between 6-12 fold, depending on thevariety. The degree of dehydration is regulated by the extent and combination of the above fiveoperations, in addition to the chemical composition of milk. In turn, the levels of moisture andsalt, and pH and cheese microflora regulate and control the biochemical changes that occur duringripening and hence determine the flavor, aroma and texture of the finished product. Thus thenature and quality of the finished cheese are determined to a very large extent by themanufacturing steps. However, it is during the ripening phase that the characteristic flavor andtexture of the individual cheese varieties develop.

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Fig 5.1 General protocol for cheese manufacture

5.3 Selection of MilkThe quality of milk has a profound effect on the quality of cheese made from it. The compositionof cheese is strongly influenced by the composition of the milk, especially the content of fat,protein, calcium and pH. The constituents and composition of milk are influenced by severalfactors, including species, breed, individual variations, nutritional status, health and stage oflactation of milk-producing animals. Owing to major compositional abnormalities, milk fromcows in the very early or late stage of lactation and those suffering from mastitis should beexcluded. Somatic cell (leucocyte) count is a useful index of quality. It is safe to say that allchanges brought about by mastitis are bad from cheese making standpoint. The bad effect ofmastitis is due almost entirely to the changes in the chemical composition of the milk. Thefirmness of the rennet coagulum or cheese curd is enhanced by: a) acidity, b) high calcium and c)high casein content. It is reduced by alkalinity, low casein, high albumin plus globulin and highsodium. Mastitis nearly always changes the composition of milk in this direction and so leads toweak curd formation. Some genetic polymorphs of the milk proteins have significant effect oncheese yield and quality and there is increasing interest in animal breeding for desirable18

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polymorphs. The milk should be free of taints of chemicals and free fatty acids that cause offflavors in the cheese, and antibiotics that inhibit bacterial cultures.A major cause of variation in the characteristics of cheese is the species of dairy animals fromwhich milk is obtained. The principal dairying species are cattle, buffalo, sheep and goats, whichproduce 85%, 11%, 2% and 2% of commercial milk, respectively. Goats and sheep are significantproducers of milk in certain regions, e.g. around the Mediterranean, where their milk is usedmainly for the production of fermented milks and cheese. Many world famous cheeses areproduced from sheeps milk, e.g. Roquefort and Feta and Romano; traditional Mozzarella is madefrom buffalo milk. There are very significant differences in the composition and physicochemicalproperties of milk, which are reflected in the characteristics of cheese, produced therefrom. Somevarieties are always made from the milk of a particular mammal. Whereas the caseins of alltyrogenic milk (capable of being converted into cheese) are much the same, the fats of this milkmay differ significantly in the proportions of the fatty acids in the triglycerides. The medium chain(C6 -C10 ) fatty acids liberated during ripening are markedly more peppery or biting in flavor thanthe very short (C2 -C4 ) or longer (C12 -C18 ) fatty acids. As it is known that cheese flavor is due to fatbreak down, it might be expected that varieties made from the milk of those mammals containinga higher proportion of C6-C10 fatty acids would develop a characteristic peppery flavor, as seen inRoquefort, which is always made from sheep milk. There are significant differences in milkcomposition between breeds of cattle, which influence cheese quality.The milk should be of good microbiological quality, as contaminating bacteria are concentrated inthe curd and may cause defects or public health problems. However, cheese milk is usuallypasteurized or subjected to alternate treatments to render it free of pathogenic, food poisoningand/or spoilage bacteria.5.4 Inhibitory Substances in MilkAll cheeses depend on the growth of lactococci and all matured cheese depe nds on thedevelopment of lactobacilli. It has been known for a long time that milks behave differently in theway lactic acid bacteria grow in them. Most important in cheese making is the slow growthof Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris in some milk, especially rawmilks. One of the factors may be the presence of a group of inhibitory substances naturallyoccurring in milk. It has been reported that a substance called lactenin found in milk may inhibitthe growth of certain streptococci. Lactenin has been shown to have two components, L1 and L2.L1 is present in colostrum and is inactivated by heating to 70C for 20 min and L2 present in mid lactation milk and is inactivated by heating to 70C for 20 min.The presence of antibiotics in milk has been a major cause of trouble in cheese making. Penicillinand other antibiotics used to control mastitis in cows find their way into milk and inhibit thegrowth of starter organisms. The best method to control this problem is to exclude such milk forcheese making. Alternatively, starters resistant to antibiotics should be used. Also enzymes suchas penicillinase can be used to neutralize the antibiotics.Preservatives like formalin, hypochlorite, quaternary ammonium compounds and otherdisinfectants present in milk may inhibit the growth of starter organisms.5.5 Storage of Chilled MilkIn modern commercial practice, particularly in Western countries milk for cheese is normallychilled to 4-5C immediately after milking and may be held at about this temperature for several19

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days on the farm and at the factory. Apart from the development of an undesirablepsychrotrophic microflora, cold storage causes physicochemical changes (e.g. shift in calciumphosphate equilibrium and dissociation of some micellar caseins), which have undesirable effectson cheese making properties of milk.5.6 Standardization of MilkThe composition of cheese is prescribed in Standards of Identity with respect to moisture and fatin dry matter, which in effect defines protein:fat ratio. Fat and casein together with moisture left inthe curd control cheese yield, but fat also has a marked influence on appearance and feel of thecurd and cheese. When ratio of casein to fat is high, the curd is more leathery and the final cheesedoes not acquire the mellow, velvetiness of a whole milk cheese. Skim milk cheeses are usuallyconsumed green. In general, the casein:fat ratio (C/F ratio) in milk should be about 0.7 for goodquality cheese. Depending on the ratio required, it can be modified by: Removing some fat by natural creaming or centrifugation, Adding skim milk, Adding cream, Adding milk powder, evaporated milk or ultrafiltration retentate.Such additions also increase the total solids content of the milk and hence increase the yield ofcheese curd per unit volume.5.7 Heat Treatment of MilkTraditionally, cheese was made from raw milk, a practice that was almost universal until the1940s. Although cheese made from raw milk develops more intense flavor than that producedfrom pasteurized milk, the former is less consistent and poses a public health risk. When cheesewas produced from fresh milk on farms or in small, local factories, the growth of contaminatingmicroorganisms was minimal but as these factories became larger, storage of milk for longerperiods became necessary and hence the microbiological quality of milk deteriorated and varied.Thermization of cheese milk is fairly widely practised on receipt at the factory to reduce themicrobial load and extend the storage period. Pasteurization of cheese milk became widespreadabout 1940, primarily from public health reasons, but also to provide a milk supply of moreuniform bacteriological quality. Although a considerable amount of cheese is sti ll produced fromraw milk, especially in Southern Europe (including such famous varieties as Swiss and Emmental)pasteurizedmilkisgenerallyused,especiallyinlargefactories.Pasteurization alters the indigenous microflora and facilitates the manufacture of cheese of moreuniform quality, but unless due care is exercised, it may damage the rennet coagulability andcurd-forming properties of milk. Even when properly pasteurized, Cheddar cheese (and probablyother varieties) made from pasteurized milk develops a less intense flavor and ripens more slowlythan raw milk cheese. Several heat induced changes, e.g. inactivation of indigenous milk enzymes,killing of indigenous microorganisms, de-naturation of whey proteins and their interaction withmicellar -casein, perhaps even shifts in salt equilibria and destruction of vitamins, could beresponsible for these changes. Until now it has not been possible to establish which of these factorswas principally responsible for the differences in quality between raw and pasteurized milkcheese. Therefore, normally sub pasteurization temperature is preferred to heat cheese milk,20

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which is termed as thermization. Thermization (65C/15 s) of cheese milk on arrival on factory is

common or standard practice in some countries. The objective is to control psychrotrophs andmilk is normally pasteurized before cheese making.5.8 Ripening of Milk (Acidification)The increase in acidity in the milk to be used for cheese making known as ripening is usuallybrought about by starter culture. Acidity developed inhibits the growth of undesirable organismsand influences the rate of coagulation. When the desired acidity (0.01% increase) is reached, mostvarieties of cheese require the addition of rennet to the ripened milk in order to obtain a curd ofthe desired characteristics. Acidification is normally via in situ production of lactic aci d, althoughpreformed acid or acidogen (gluconic acid--lactone) are now used to directly acidify curd forsome varieties, e.g. Mozzarella cheese, UF Feta and Cottage. Until recently, the indigenousmicroflora of milk was relied upon for acid production. Since this was probably a mixedmicroflora, the rate of acid production was unpredictable and the growth of undesirable bacterialed to the production of gas and off-flavors. It is now almost universal practice to add a culture(starter) of selected lactic acid bacteria to pasteurized cheese milk to achieve a uniform andpredictable rate of acid production. For cheese varieties that are cooked to not more than 40C, astarter consisting of Lactococcus lactis subsp. lactis and/or Lc. lactis subsp. cremoris is normally usedwhile a mixed culture Streptococcus salivarus var.thermophilus, Lactobacillus spp. (L. bulgaricus, L.helveticus, L. casei) or lactobacillus culture alone is used for varieties that are cooked to highertemperature, e.g. Swiss, hard Italian varieties.5.9 CoagulationThe essential step in the manufacture of all cheese varieties involves coagulation of casein of milkto form a gel, which entraps the fat, if present. Coagulation may be achieved by: Limited proteolysis by selected proteinases (rennets) Acidification to pH 4.6 Acidification to pH 5.2 and heating to 90C.Most cheese varieties, and about 75% of total production, are produced by rennet coagulation butsome acid coagulated varieties, e.g. Quark and Cottage cheese, are of major importance. The acid/heat coagulated cheeses are relatively minor varieties which are usually produced from rennetcheese whey and a blend of whey and skim milk and evolved as a means for recovering thenutritionally valuable whey proteins; they are usually used as food ingredients. Importantvarieties are Ricotta (Italy), Anari (Cyprus) and Manouri (Greece). A fourth minor group of cheeseis produced not by coagulation, but by thermal evaporation of water from a mixture of whey andskim milk, whole milk or cream and crystallization of lactose (e.g. Mysost).Rennin is milk-curdling enzyme, which is usually obtained from the fourth stomach (abomasum)of suckling calves. In other animals, the proteolytic enzyme, pepsin, substitutes rennin. Rennin isprepared commercially for use in cheese making as a salt extract of dried calf stomach. Such anextract containing the enzyme is called rennet or rennet extract.Rennin is an extremely powerful clotting enzyme; one part of pure rennin can clot more than fi vemillion parts of milk. The optimum pH for rennin action on milk is 5.4 and for pepsin it is 2.0.However, it can function very powerfully as a clotting agent at almost neutral pH (6.2-6.4). The21

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ratio of clotting to proteolytic power is very high in case of rennin, but is lower in case of pepsinand other proteolytic enzymes tried in cheese making. The latter type of enzymes result in a bitterproduct. For hard cheese such as Cheddar, usually about 2.5 g of commercial rennet powder isused for 100 l of milk. In case of Meito rennet it is 1.65 g/100 l milk.The formation of curd depends upon the coagulation of the casein in milk. With rennet this occursin two steps. The calcium caseinate in milk is first changed to the paracasein, which then combineswith the calcium ions present in the milk to form an insoluble curd. This curd is elastic and whenheated or pressed it will shrink, squeezing out most of the retained whey. Slow development ofcurd may be due to too little rennet or to the use of overheated milk. In the latter case, the additionof small amount (0.02%) of calcium chloride to the milk usually will restore the calcium ionbalance and permit the normal functioning of rennin. No satisfactory substitute for rennin hasbeen found but at times other milk clotting enzymes, such as pepsin, papain, and microbial andrecombinant rennets have been used.Rennet extract is diluted up to 20-30 times with clean potable water before added to the cheesemilk. After addition of rennet, the milk is stirred for about two minutes to distribute the rennetthoroughly, and then currents are stopped in the milk with a paddle or rake. Vibration of the vatmust be prevented during setting. Steam leakage into the jacket of the vat during setting should beavoided. The milk is then left undisturbed for the curd to form, and this becomes apparent inabout 15 min. After about 30 min the milk is set with a firm curd.5.10 Post-Coagulation Processing OperationsOne of the main reasons for the great interest in studying rennet coagulation is to optimize the gelcutting time. When the gel (coagulum) is firm enough, it is cut by mechanical knives in both thehorizontal and vertical directions to produce curd particles. In cheese making, the cutting rangebetween 20 and 50 min, depending on:1. Concentration of rennet used, e.g. 20 ml of single strength rennet per 100 l milk, although thisdepends on the strength of the rennet used and the other coagulation conditions.2. Whether CaCl2 is added, as this accelerates clotting (the maximum legal level in many countriesis 0.2%)3. Coagulation temperature (coagulation occurs faster at higher temperature)4. pH (the activity of chymosin decreases with an increase in pH)5. Seasonal changes in milk composition; e.g. late-lactation milk can be slow to clot due to its highpH and hydrolysis of caseins within the mammary gland by plasmin. Low levels of plasminhydrolysis reduce RCT and increase the initial rate of aggregation of rennet-altered micellesalthough final gel strength is reduced.6. The quality of the dilution water used to make the rennet solution prior to the addition ofcheese vat, as both excessive chlorine and a high level of water hardness can adversely affectactivity.

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5.11Cutting the Coagulum

The rennet gel is quite stable if maintained under quiescent conditions but if it is cut or broken,syneresis occurs rapidly, expelling whey. Syneresis concentrates the fat and casein of milk by afactor of about 6.012, depending upon the variety. The rate and extent of syneresis are influencedby milk composition, especially Ca++ and casein, pH of the whey, size of cutting of cubes, cookingtemperature, rate of stirring of the curd-whey mixture and time. The composition of the finishedcheese is to a large degree determined by the extent of syneresis and since this is readily under thecontrol of the cheesemaker, it is here that the differentiation of the individual cheese varietiesreally begins, although, the composition of cheese milk, the amount and type of starter and theamount and type of rennet are also equally significant.The coagulum is ready to cut after a period of from 25 min to 2 h, as defined by the recipe. Thedetermination of exact time of cutting is very critical for the quality of cheese. However, the cheesemakers attempts to judge the exact point of cutting are fraught with difficulties. The surface layerof coagulum is often some degree colder than the coagulum underneath and is, therefore, softer.To judge firmness of curd on the surface, therefore, has little meaning.The main method employed by cheesemakers is to plunge the hand, rod or thermometer stembelow the surface layer and to lift the coagulum causing it to break in a cleavage line. A clearcleavage with green whey at the base of the cleft indicates that the curd is ready to cut. A softirregular cleavage with white whey indicates that the curd is too soft. The sides of the cleft showthe quality of the curd. Granular curds indicate that the curd is too firm. A rule used by somecheesemakers is that the curd should be cut earlier rather than later, and once cut; the curd shouldbe left to complete its forming process in the warmer whey which rises over it. If the coagulumbecomes too firm, knives or curd breakers crush the curd rather than cut it cleanly. When curd isready for cutting, it is first cut horizontally and then vertically. This sequence is essential to followbecause if the curd is cut vertically first, slabs so made will not have sufficient strength to standand thus, will shatter.The curds, which have been cut cleanly, will heal or join up the cut fibrils on the new curdsurfaces and thus prevent loss of fat and other milk components. Surface-active materials such asphospholipids and whey proteins accumulate on the cut surface and form a thin osmoticmembrane. This membrane controls the whey expulsion during cooking.The fat globules are held in the matrix of the casein network, partly by physical enclosure andparty by loose bonding of the globule membrane and protein. Fat globules near the cut surfacesleak away. Such fat although only 0.2-0.3% in the whey, is really 10% of the original fat in the milkand leads to loss of cheese yield. The whey from the cut curds carries water-soluble componentsincluding lactose, whey proteins, salts, peptides and other non-protein nitrogenous substances.The size of the curds after cutting depends on type of cheese to be manufactured. Thus curds,which need to be scalded to higher temperatures, are cut into smaller pieces, while those curds,which are scalded to lower temperatures, can be left in large pieces unless the curds are very acid.Curved-wire-strung, harp-like curd breakers are used manually in the smaller cheese dairies. Thelarger installations use multibladed, hand held steel knives. The blades vary from 6-18 mm apartand 76 cm long. Some cutters are composed of wires strung on steel frames.Mechanically operated curd knives are larger than the manual knives and use either blades orwires. It is very important that the edges of the blades are kept sharp enough to cut cleanly. Heavy23

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gauge wires tend to tear the curd more than steel knives, and some cheesemakers cut slightlyearlier with wires than the knives.Cutting the coagulum lengthwise once manually in the long rectangular vats normally cut bymechanically operated knives prevents crushing of the soft curds during the first mechanicalcutting. The rotating knives in round or oval vats do not crush the curd against the vat sides. Evenso, the speed of rotation in some equipment can be controlled. The angle of the blade presented tothe curd is such that if the rotation of the knife is reversed it stirs rather than cuts the curd.5.12 CookingThe curd, when first cut, is soft and the coat surrounding the particles is open. Stirring the curdgently until the first flush of whey has left the curd particles is necessary to prevent unduecrushing and loss of fat and curd dust. Once the curd coat becomes more membrane-like theagitation rate can be increased.Cooking or scalding the curd causes the protein matrix to shrink and expel more whey. Theincrease in temperature also speeds up the metabolism of bacteria enclosed within the curd. Lacticacid production increases, pH declines, and acidity assists in shrinking the particles to e xpressmore whey.Since the whey has, in solution, lactose and salts, the amount of these substances retained in thecheese is proportional to the amount of moisture in the curd. The calcium phosphate associatedwith the casein and in colloidal state, will gradually become solubilized as the pH falls. Thus, highacid curds (i.e. blue veined cheese curds) lose more calcium (92%) than low acid curds such asEdam (35%).Lactose is the main metabolite of the lactic acid bacteria in the curd for the production of lacticacid. Since lactose must cross the cell wall membrane, it is not only the presence of lactose but alsothe strength of the lactose solution, which is a controlling factor in the metabolism of the bacteria.Thus, once the lactose concentration has decreased to a certain point, then much smaller decreaseshave greater effect on the growth of bacteria and on the production of lactic acid. The cheesemaker has control over lactose in the curd, and, therefore, the amount of lactic acid formed,through the size of the curd particles, scald temperature and the rate of rise of temperature of thecurds. There are two methods of reducing the amount of lactose in the cheese curds:1. Shrinkage of the curds brought about by heat and lowering of the pH owing to development oflactic acid in the curd.2. The addition of water to the whey, which increases the osmotic effect across the curdmembranes and thus extracts the lactose from the curd moisture into the diluted whey.The addition of hot water to the whey/ curd mixture is used as a method of scalding (heating) thecurd in the washed curd cheese processes.The aim of scalding the curd is to shrink the curd to expel moisture and so firm up the curd to astate ready for texture formation, pressing or salting. This state provides the dividing betweenfour main groups of cheese (excluding soft cheese, some of which may be scalded).1. The textured cheese like Cheddar, Cheshire.

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2. The pasta filata types or kneaded cheese.

3. The cheese untextured in the vat stage, like Edam and Gouda cheese, and also those whichacquire texture later, like Tilsiter, Emmental, etc.4. Blue veined cheese.The variation of scalding rates is carried out according to the acidity produced and is under thecontrol of cheesemaker. This is a further point in the recipe where previous experience aids ininterpretation. A high rate of scald will shrink the coat of the curd particles so much that themembrane is so firm that moisture is locked in the curd. The resultant cheese is acid, harshtexture, crumbly and eventually dry.Low rates of scald may be necessary for curds in which the bacteria are slow to produce acid.Alternatively, curd shrinkage may be by acid alone without the use of scald. The recipedetermines the maximum scald temperature but it is important to note that the normal lacticstarter bacteria will be inhibited, if not destroyed, if the scald temperature is too high (i.e.temperature beyond 40C). Scald temperatures higher than normal need the inclusion of hightemperature-enduring starter bacteria (i.e. S. thermophilus, L. bulgaricus, etc.). Although lactose,being soluble tends to leave the curds to be concentrated in the whey, there may be reversemovement back into the curd if the curd and whey acidities are too different.The cheesemaker has a decision to make in respect of when to cease stirring the whey curdmixture; this is not often included in the recipe. The cessation of the stirring is called the pitchingpoint when the curd sinks down to the bottom of the vat.Normally, fast acid curds are stirred until the whey is removed. With very slowly developingcurds, the stirring ceases altogether and the curd is pitched, or sometimes, to prevent excessivematting of the curd into lumps, the curds are stirred at intervals.5.13 Curd TreatmentThe manner in which the curd is handled varies in some degree according to the kind of cheese tobe made. The acidity of the curd continues to increase and its body becomes firmer owing to adecrease in its content of whey. Heating the curd favors these reactions. If a soft high moisturecheese is made, the curd is removed from the vat quickly and the whey is drained. For somevarieties of cheese, the curd is cut and stirred in the whey while it is being heated. For Che ddartype cheese, the curd is heated in the whey and allowed to form continuous mass, which is thencut and milled into small pieces before further processing.The manner in which the whey is drained from the curd varies with the kind of cheese:1. Cream cheese, for example, is prepared by placing the curd on cloths which allow the whey todrain away.2. Sometimes the curd is placed in forms or hoops put on mats or coarsely woven screens whichallow the whey to drain as in the manufacture of Brick cheese,3. In the making of Cheddar cheese, curd is allowed to sink in the vat and the supernatant whey isdrawn off,

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4. In making Swiss cheese, the curd is separated by placing a cloth under the curd and lifting it outof the vat or kettle.The rate at which the whey is allowed to drain away is determined by the kind of cheese beingmade. Acid continues to develop in the curd as long as appreciable amounts of whey are present.With the increase in acidity the curd becomes elastic and can be stretched or, if heated, it can bedrawn out into silky strings. This is the basis of practical test used by makers of Cheddar cheese. Ahot iron rod is touched to the curd, and as it is drawn away, the length of the curd fibers at theirbreaking point is noted, the higher the acidity the longer the threads.5.14 PressingThe last portion of the whey is removed from the curd by pressing. This operation is also used tomould some varieties of cheese in their conventional shape. The degree of pressure used varieswith the kind of cheese.The curd is composed of a matrix of protein enclosing fat globules, moisture, lactose, salts, nonprotein nitrogenous substances, as well as peptides. The curd also contains air and some gas (CO 2 )so that while it is warm it is springy, elastic and soft. The fat is also mainly in the liquid state. Salt(NaCl) may or may not have been applied and salt will dissolve some of the casein surfaces, andalso releases water. Thus the surface layer of casein may be rendered hard and horny if the salt i snot allowed to dissolve freely into the warm curd.Pressing the curd should, therefore, be gradual at first, because high pressure at first compressesthe surface layer of the cheese and can lock moisture into pockets in the body of the cheese. Thetemperature of the curd before pressing should be below the liquid fat temperature, i.e. 23.9C insummer and 26C in winter. Otherwise, fat will leak from the curd and be lost in the whey, or willfill spaces in between the curds and give a greasy cheese. The pressure applied to the cheeseshould be per unit area of the cheese and not per cheese, which may vary with size. Table 5.1shows the pressure, traditionally applied and a comparison with pressures applied to 18 kg blockcheese.Since the cheese curd holds a volume of air before pressing, those cheeses requiring very closedcurds (e.g. Cheddar) have been pressed under a vacuum of 85-95 kN/m2 (25-28 in Hg). Thevacuum applied for only a short time (2-3 h), also assists in cooling the curd.Pressures have been traditionally applied for 2-3 days to Cheddar cheese, but the more recentblock cheese pressing has been limited to 24-36 h, and with vacuum pressing, 10-15 h. This hasenabled the cheese mould to be washed and reused the following days.Cheese presses are either spring, dead weight, pneumatically or hydraulically operated. Recently,the larger ton or box presses have been used. The presses have vacuum cylinders so that thecurd can be pressed under vacuum.One of the requirements of the pressed cheese is that the outside (rind) surface is close, smoothand with no crevices for mold penetration. The traditional methods used coarse Hessian cloths toassist in closing up the holes in the curd. Sometimes, the cheese was immersed in hot water at48.9C to plasticize the coat and the cheese was then repressed in stiff Calico cloth to obtain a closefinish.These systems were highly labour intensive, and textured synthetic films have replaced the cloths26

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previously used. Traditional cheesemakers and certain cheese buyers still prefer the oldermethods of cheese preparation, especially for the texture cheese varieties such as Cheddar,Cheshire etc.Table 5.1 Pressures applied to cheese of various sizes

5.15 Treatment of Rind

The manner in which the surface of the cheese is treated also influences its characteristics, forexample, frequently cleaning the rind, for Cheddar.1. Cheddar and Swiss cheeses are given a smooth and uniform surface or rind by pressing thecurd while it still is warm, and curing the cheese under conditions that allow the moisture toevaporate from the surface2. The activity of organisms on the surface is prevented in Swiss cheese by frequently cleaning therind. For Cheddar cheese, this is done by coating the cheese with paraffin wax and holding it in acool room with low humidity,3. Holding them in cool, moist environment encourages the growth of mold on Camembert andRoquefort type cheeses, and the growth of yeasts and bacteria on Brick and Limburger cheeses.The soft types of cheese acquire a rind during ripening, often as a result of the growth of moldsand bacteria. Later, the evaporation of moisture hardens the rind so that it is more rigid to handle.In many instances the rind is kept clean by repeated washing with a salt impregnated cloth (e.g.Emmental) or repeated brushing to remove mould growth (e.g. Cantal). When these cheeses areripe and ready for sale, the rind is simply coated with vegetable (olive) oil, which may be coloredbrown or black (e.g. Parmesan, Romano).Smoking of cheese also gives the coat a fatty layer and has a preservative effect, due to phenoliccompounds from the smoke. Spices are also used on the coats of some cheese to impart a flavor tothe curd, but mainly the spices are included in the curd. Feta and similar cheeses are packed incasks or drums filled with brine or salted whey.Gorgonzola has also been coated with Plaster of Paris as a protective coat inside a woven basket.The plaster is not completely airtight and allows the cheese to breath and mold to remain blue.

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The larger hard-pressed cheeses, like Cheddar, Emmental, etc. have in recent years been producedin block shapes for two main reasons:1. The packing of cheese in retail markets for consumer sale in small portions has accelerated theuse of block cheese shapes. These cheese blocks range from 10 to 20 kg in weight, are rectangularand can be cut mechanically without waste into consumer portions.2. The second reason is with respect to mold or cheese mite damage, which has caused serious lossin traditional round-shaped cheese.Attempts to overcome these defects first employed, and still use, chemical treatments, i.e. sorbicacid and its salts, or pimaricin to stop mold growth, and/or waxing or resinous coating of thecheese rind to prevent both mould growth and mite infestation.Waxing of cheese, like Cheddar, Cheshire, etc. over the bandage requires that the bandage iscompletely dry (2-3 days drying). If the bandage is not dry the wax coat eels away and is noteffective as mold preventive. The waxes used are available with different melting points, from 4982C, for either temperate or tropical usage. The application of wax is usually by dipping thecheese in a bath of melted wax for up to 30 s and then allowing it to cool quickly. It may benecessary to dip twice if the cheese is not totally covered on the first occasion.5.16 SaltingSalting of perishable foods is among the most ancient and widely practiced techniques of foodpreservation. Salt has achieved universal acceptance as a mineral of great importance in trade andindustry, and, in view of its preservative qualities, it has become a peculiarly appropriate symbolof fidelity in many cultures. It is, therefore, no surprise that salting is a key element in thatcombination of techniques that has evolved for preserving the solids of milk in the form of cheese.Common salt (NaCl) is an ingredient of practically every variety of cheese. It may be added tosubdivide cheese curds, as is the case with Cheddar and related types, or apply by immersion ofthe formed cheese in brine, as for Gouda, Swiss, Feta and related types. For some cheeses, the saltis rubbed on the surface after moulding is complete and, for a few types (e.g. Domiati), some or allof the salt is added to the cheese milk before curd production commences. The presence of salt incheese and the manner of its incorporation has a significant impact on the course of the cheesefermentation, and on the final characteristics of the cheese as consumed.The salt in cheese: Draws the whey out of the curd, Suppresses the proliferation of unwanted microorganisms, including pathogens, Regulates the growth of desirable organisms, including lactic acid bacteria (acidity, oxygentension and temperature also regulate the growth of these organisms), Promotes physical and chemical changes in the maturing cheese, Directly modifies taste, and

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Serves as a factor in control of acidity.

The salt in cheese is held in solution in the aqueous phase and its concentration in solution is astrong determinant of much of the biological and biochemical changes that occur during cheesematuration. The actual level of salt in cheese varies with the type, ranging from 0.5% to about 3%(w/w) but this range is amplified by the wide differences in water content between cheesevarieties, such that the concentration of NaCl in the aqueous phase may range from less than 1%to about 8%. The level of salt in cheese, the manner of its addition and the joint impact of thesefactors on the time needed for equilibration of the salt concentration in the aqueous phase are keydeterminants of varietal differences in cheese characteristics.Within any one cheese, the distribution of salt may vary considerably according to the method ofapplication. Dry salted cheese, such as Cheddar, should have uniform salt levels throughout thebody within just a few hours after salting, whereas for brine-salted cheese, there is a markeddifference between the salt content of the surface and the interior, which persists for many days orweeks, dependent on the dimensions of the cheese. Rapid attainment of salt uniformity within drysalted cheese curds generally slows or stops fermentation of the residual lactose, leaving a pool offermentable carbohydrate to support the growth of the more salt-tolerant strains of the starterbacteria and/or the growth of the non-starter lactic acid bacteria (NSLAB), with a potentiallyprofound impact on the course of maturation. A low internal salt level in brine -salted cheeseallows for continuation of the fermentation by the added starter organisms of practically all of thelactose to lactic acid and associated end products, thus leaving little fermentable carbohydrate tosupport the growth of NSLAB, resulting in a different course of maturation and different flavorprofiles.5.16.1 Methods of saltingThere are three main techniques for salting of cheese: Mixing of dry salt crystals with subdivided cheese curds prior to the moulding/pressing stageof manufacture, Immersion of the moulded cheese in a brine solution, Application of dry salt or salt slurry to the surface of the formed cheese.For a number of varieties, a combination of these techniques is used, and for a few cheese types,salt is added either to the milk or the whey.Brined cheeses are formed into their final size and shape prior to being immersed in a solution fora period ranging from a few hours to a few days in vat containing circulating or static brine. Staticbrine systems usually have un-dissolved salt at the bottom of the vats and stirring must be carriedout frequently. Circulating systems have means for automatically maintaining the strength of thebrine. Brine concentration typically ranges from 15% to 25% (w/w) NaCl in water andtemperature may vary from about 8 to 20C.The salting time depends primarily on the desired salt content, and is further influenced by: Brine temperature (Diffusion rate increases with temperature)

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Salt concentration (Higher concentration gives faster salt uptake, but more extreme variationswithin the young cheese) Cheese dimensions (Smaller and flatter cheeses take up salt more rapidly; spherical cheeses takeup salt more evenly) Cheese moisture and pH (Higher moisture and pH both lead to more rapid salt intake).

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Module 3. Milk quality in relation to cheese making

Lesson 6SELECTION AND COMPOSITION OF MILK6.1 IntroductionCheese making commences with the selection of milk. The quality of raw milk used for cheesemaking has an important bearing on the quality of cheese resulting from it. Milk qualityinfluences starter growth, rennet coagulation, manufacturing methods, development of taints andother defects in body and texture of cheese and other changes taking place during ripening ofcheese. Milk quality is assessed in terms of sensory, microbiological and chemical qualityattributes. As soon as milk is received at the reception dock of the cheese factory, it is evaluatedfor its odor and appearance. It must not possess any objectionable odor and must be free fromextraneous matter. Once the milk has been accepted for further processing, it is assessed for thefollowing group of factors.6.2 Quantitative Factors6.2.1 Composition of milkThe composition of milk affects mainly the yield and texture of cheese. The composition of milkaffects coagulum properties thereby influencing yield and texture. The milk constituents of primeimportance in cheese making are milk proteins (particularly casein), milk fat and mineral salts(particularly calcium). Influence of each of these factors on cheese making is discussed below:6.2.1.1 Milk proteinsCasein, the major milk protein, exists largely in micellar form in milk. It constitutes about 70-80%of the total milk protein. The casein micelles are composed of -casein, -casein, -casein andsome minor components. In addition, genetic variants of these components are also found. Thecomposition and concentration of such a mixture is not constant and subjected to variations due toinfluence of species, breed, animal health, stage of lactation, climate, time of year andenvironmental factors. These alterations in the concentration of total casein, relative proportion ofits constituents and genetic variants, size of the casein micelle and mineral make up of the caseinmicelles affect cheese making properties of milk such as clotting time, curd strength, syneresis,cheese yield, proteolysis of cheese and composition of the cheese.During cheese making, serum proteins and lactose are lost in whey. So, milk high in casein isdesirable. Milk high in whey protein content may delay clotting time as -lactoglobulin undergoesaggregation when subjected to heat and may react with -casein. Apart from longer clotting time,the interaction between -lactoglobulin and the casein tends to cause softer curds which losemoisture more slowly. Cheese milk containing B variant of -and -casein give shorter clottingtime, higher curd strength as compared to the milk devoid of this variant. Size of the caseinmicelle also affects clotting time. Smaller micelles having more -casein give shorter clotting timethan the larger ones.

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6.2.1.2 Milk fat

The amount, composition and nature of milk fat are affected by the same factors as discussed inthe case of milk proteins. Alterations in milk fat composition and the amount of milk fat havedirect influence on cheese making characteristics and quality of cheese like rennet coagulationtime (RCT), coagulum strength, syneresis, yield, flavor and texture of cheese and cheesecomposition.Increase in the fat content of milk gives reduced syneresis and thus longer times are required toachieve desired moisture content in cheese. Too low fat in milk is also not desirable as it posesproblem of moisture retention and results in hard and dry body cheese. Texture of cheese is alsoaffected by the fat content. Low fat milk gives cheese with leathery texture and lacks mellow,velvetiness while high fat milk produces too soft, buttery and greasy texture. Fat is also importantfor flavor development of cheese. During ripening, lipolysis of fat results in formation of fattyacids, which impart to cheese, its peculiar flavor.The physical and chemical nature of milk fat also plays a significant role in cheese making. Fat isincorporated in the casein matrix. This incorporation of fat is dependent on size of fat globule andits composition. Smaller sized globules are easy to incorporate in curd than larger ones. Milk fatwith higher melting point is better incorporated in the curd.The milk used for cheese making must be of uniform quality in terms of its fat and casein content.So, it is always desirable to pool all the milk supply prior to standardization to a definitecasein/fat ratio. In case of Cheddar cheese making, milk is standardized to a casein/fat ratiobetween 0.67 and 0.72.6.2.1.3 Milk saltsThe milk salts are normally classed as ash. Ash contains a large proportion of the metalliccomponents, potassium, sodium, calcium, zinc, chromium, and nickel as well as the non-metallicelements such as sulphur, chlorine, phosphorous, iodine, etc. The salts in milk which are ofprimary importance to the cheese making process are calcium and magnesium salts of phosphoricand citric acid. Calcium makes casein complex with phosphates. Calcium content of milk greatlyinfluences rennet coagulation time, strength of the clot and body and texture of cheese. Thequantity of calcium affects the size of the casein aggregates. More calcium content i n milk leads toincreased micelle size of the casein. Variation in concentration of calcium as well as magnesium,phosphates, citrates and sodium has a direct influence on RCT of milk. High soluble phosphates,citrates and sodium and low soluble calcium and magnesium and also low proportion of caseinbound calcium have been found to give slow coagulation of milk by rennet.6.2.2 Qualitative factorsChemical qualities of milk which affect the cheese quality fall into three main groups:A. Quality that inhibits starter growthB. Quality that affects coagulationC. Quality that produces taints, gas-holes, etc., in cheese.Starter is said to be 90% of importance of cheese making. This statement emphasizes theimportance of starter organisms in cheese making. Therefore, the milk used for cheese must befree from inhibitory substances of physiological origin, preservatives, and antibiotics. Presence of32

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even 0.01 IU/ml antibiotics in milk can affect the starter growth.In cheese making one of the most important factors is the time taken for coagulation of milk withrennet. Mixing of mastitis milk, colostrum or late lactation milk adversely affects the coagulation.Therefore, milk must be free from these contaminants.Mastitis milk is high in serum albumins and often high in sodium and chloride content as well. Itis low in fat, casein, lactose, phosphate, potassium and calcium content than the normal milk.Since it is low in casein it produces low yield and moist cheese. It has high concentration ofimmunoglobulins, several enzymes (e.g. proteinase, protease-peptone and catalase) and leucocytecount. Content of short chain fatty acids are more. Lipolysis in milk increases with initial count,but later decreases with high cell count. Mastitis milk has a changed casein composition like less-casein, more and -casein, presence of para-- casein in comparison to good quality milk.Late lactation milk resembles sub-clinical mastitis milk biochemically. It is slightly alkaline, highin albumin and chloride and low in casein, lactose and calcium and its effect on coagulation ofmilk with rennet is similar to that of mastitis milk.Colostrum is grossly different from the normal milk. It is very rich in proteins, vitamin A, andsodium chloride, but contains lower amounts of carbohydrates, lipids and potassium than normalmilk. It contains many antimicrobial substances like lactoferrin and lactoperoxidase (LP), whichinhibit starter cultures used in cheese making. Therefore, colostrum must not be mixed with themilk at least for three days but preferably up to 15 days to avoid coagulation delays.6.3 Natural Inhibitory Substances and Antibiotic Residues in MilkRaw milk contains a number of natural inhibitory systems such as immunoglobulins, lactoferrin,lysozyme and LP system. Presence of such inhibitory systems in milk can influence cheese makingproperties, particularly starter growth and acid development. Other than these natural inhibitors,some antibiotics may also gain entry to milk as a result of the medical tre atment of animals forvarious diseases. The presence of antibiotics again affects acid development and may also causestarter failure leading to various defects like high moisture in cheese, early and late blowing, weakand pasty body, cracks, open texture and sponginess.

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Lesson 7MICROBIOLOGICAL QUALITY OF MILK7.1 IntroductionCow milk is the commonly used source for cheese making all over the world. The microbiologicalquality of raw milk reaching the cheese factory is controlled by the following H factors.(i) Health of the milch animal.(ii) Hygiene during milk production (hygiene of farm, personnel and equipments/utensils).(iii) Handling and refrigeration.Clean milk secreted from the udder of the healthy animal contains only few numbers ofmicroorganism (< 10,000/ml). Milk obtained from mastitis cow may contain high numbers ofmicroorganism as well as leucocytes depending on the severity of infection. Maintenance ofhygienic practices during milk production at farm is an important aspect of clean milk production.Cleaning and sanitization of milk contact surfaces directly determine the extent of contaminationof milk after it has been drawn from the udder.The post production hygienic handling of milk and proper refrigeration can check theproliferation of microorganisms in milk before cheese making. Milk should be held at around 4Cduring transport an in cheese plant.7.2 Microorganisms in Raw MilkThe presence and multiplication of saprophytic and pathogenic bacteria in raw milk might changethe milk composition and produce toxins, and influence the quality and safety of the milk andmilk products. Moreover, flavor of the raw milk may be adversely influenced and heat-stablebacterial enzymes may continue to act in products particularly during long storage and adverselyaffect the stability of milk and milk products. The pathogenic bacteria include classicalmicroorganisms and emerging pathogens. At present Salmonella, pathogenic Escherichiacoli strains, Yersinia enterocolitica, Staphylococcus aureus, Listeria monocytogenes, Campylobacterjejuni are the most important.According to the main points of attack on the major milk constituents, the saprophytic bacteria aresubdivided as follows:a) Microorganisms degrading lactose are classified as glycolates, e.g. Streptococci, Lactobacilli andColiformsb) Microorganisms degrading proteins are classified as proteolytes, e.g. Pseudomonas,Enterobacteriaceae, and aerobic sporeformers.c) Microorganisms degrading lipids are classified as lipolytes, e.g. Pseudomonas, Micrococci,Aeromonas and Corynebacteria.

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The effect of growth on saprophytic bacteria in milk may be important in three ways as follows:a) The change in milk composition may interfere with manufacture, if fermentation is involved inthe manufacture process, and this may affect the yield and quality of the product.b) The flavor of the raw milk may be adversely influenced (e.g. rancidity) and this may directlyaffect the flavor of the product e.g. Cottage cheese.c) Heat-stable bacterial enzymes may continue to act in the product, particularly during longstorage, and adversely affect the stability and/or flavor of cream and UHT milk.Milk is generally held at refrigerated condition for 1-3 days before processing. The milk storedunder such conditions contains predominantly psychotropic bacteria (over one million/ml). Thecommon genera encountered are Pseudomonas, Aeromonas, Alcaligenes, lactic acid bacteria,gram positive sporeformers, coryneform group, enterococci and coliforms. The psychotropicbacteria may further increase in number due to proliferation, especially when the temperature ofthe refrigerated milk increases. These conditions facilitate the release of some heat stable(surviving pasteurization) enzymes like proteinases, lipases, and phospholipases in milk whichleads to proteolysis and lipolysis. Lipolysis of milk leads to rancidity that inhibits growth andactivity of lactic culture because of lower surface tension or specific toxic effects of certain freefatty acids (C8 -C12 fatty acids).7.3 Somatic CellsThe milk used for preparation of cheese should be from healthy animal with a somatic cell countof < 50,000/ml. If raw milk contains > 50,000 somatic cells/ml results in phagocytosization oflactic acid bacteria (LAB) leads to slow starter activity in cheese vat, increase in rennet clottingtime causing decreased curd firmness and a loose final body and texture.7.4. Antibiotic ResiduesIn lactating cows, antimicrobial agents are used mostly for the therapy of mastitis but also of otherdiseases (e.g. laminitis, respiratory diseases, metritis). Antimicrobial agents administered to cowsin the course of lactation can pass to milk in various levels and inhibit starter activity.7.5 Disinfectants and PreservativesOccasionally, chemical sanitizers may contaminate milk, usually as a result of human error.Quaternary ammonium compounds (QACs) present more potential problems, because theymaintain activity in milk, and LAB are sensitive to low concentrations. The amo unt of chemicalsanitizer that might enter milk through lack of rinsing should not be sufficient to cause cultureinhibition. However, problems can be encountered when sanitizer solution is not drained fromtanks or trucks.7.6 BacteriophagesBacteriophages (phages) are viruses that infect bacteria. Bacteriophagic infection of starter culturescan result in failure of the fermentation and loss of product. Despite implementation of controlmeasures, bacteriophagic infection still causes production problems in the modern dairyfermentation industry.

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7.7 Raw Milk Associated Inhibitors

Lactic starter cultures grow more slowly in raw than in heated milk; a phenomenon caused by thepresence of natural inhibitors. The lactoperoxidase system is the most significant microbialinhibitor in raw milk, but the presence of agglutinins is an important problem in acid -coagulatedcheeses. Other naturally occurring microbial inhibitors in milk include lysozyme and lactoferrin.

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Module 4. Pretreatments of milk for cheese making

Lesson 8CHILLING, STORAGE, CLARIFICATION AND BACTOFUGATION8.1 IntroductionFor centuries, milk for cheese making had been subjected to no pre-treatment before curdling, andmany cheese varieties worldwide are still made from raw milk. However, predominantly forreasons of safety, but also for consistency of quality and manipulation of product characteristics,most cheese making today involves the treatment of milk by one or more processing steps prior toaddition of coagulant and starter culture. Perhaps the simplest and earliest technologicalintervention, driven by safety concerns, was the pasteurization of milk. Pasteurisation inactivatessome enzymes, reverses shifts in the mineral balance of milk and influences the microflora of nonstarter lactic acid bacteria (NSLAB) in the final cheese. Pasteurization unacceptably impairs thecheese flavor as a result of its influence on NSLAB. On the other hand, more severe heattreatments than pasteurization result in significant denaturation of whey proteins and theirresulting incorporation into cheese curd, with significant effects on cheese yield and composition.This chapter deals with the effect of the various treatments given to milk on cheese quality.8.2 Chilling and Cold StorageRaw milk is sometimes cooled to about 4 oC and stored in refrigerated tanks or storage tanks priorto its conversion into cheese. This practice of storing milk at refrigerated temp erature not onlyincreases the possibility of growth of psychrotrophs but also alters the physico -chemicalproperties of milk components like casein and minerals. Due to these alterations, many propertieschange significantly like rennet coagulation time, firmness, moisture retention etc. Rennetcoagulation time increases, firmness decreases and moisture retention increases due to coldstorage of milk. The impaired technological properties as a result of chilling and cold storage ofthe raw milk can be improved by adopting measures such as:1. Acidification of cheese milk with lactic acid to pH 6.52. Addition of calcium chloride @ 0.02%3. Addition of more rennet within permissible limits4. Use of higher renneting temperature5. Use of higher cooking temperaturesAmong all above stated measures, first two have been found to be most effective.

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8.3 ClarificationClarification is one of the centrifugal processes used in dairy industries. It is used to removeleukocytes, cellular debris and particles from earth or fodder gaining entry into milk.Centrifugation of milk by the clarifier removes much of the small sized particles in milk, having aspecific gravity higher than 1.032, particularly dirt, cells and larger microorganisms if they arepresent in clumps. Clarification decreases the tendency of fat to form aggregates on standing,increases the rate of multiplication of starter organisms, may increase the fat losses in whey andmay also decrease the moisture and yield of cheese. Due to the removal of anaerobicsporeformers, marked improvement in cheese quality has been recorded.8.4 BactofugationBactofugation is a physical process through which bacteria are removed from milk, the size anddensity of bacteria being the criteria for their removal. The other factors deciding the efficiency ofbactofuge to remove bacteria are initial bacterial load, pre-treatment of milk, throughput ofmachine, volume of bactofugate to throughput, frequency of partial desludging and duration ofthe run. Bactofuge is a clarifier with one inlet for raw milk and one outlet for treated milk. Thereare 2-4 nozzles fitted into the bowl wall for the discharge of skim milk. Bacteria are subjected to acentrifugal force of the order of 7000- 9000 G. The process is also able to remove the heat resistantspores which otherwise are not removed by any other thermal process.The bactofuge system has been used in the cheese industry where its high-cleaning capabilitieshave been used to remove spores from cheese milk that could cause late fermentation in semi-hardcheeses.Effect of bactofugation on cheese making may be summarized as follows: Effective method for preventing late blowing defect in semi-hard or hard varieties of cheeses. Itis mainly due to removal of anaerobic microorganisms Facilitates reduction or elimination in the use of nitrates (nitrates are added to prevent latefermentation in cheese) Weakens the coagulum during cheese making which can be overcome by addition of calciumchloride.

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Lesson 9MEMBRANE PROCESSING OF MILK FOR CHEESE MAKING9.1 IntroductionMembrane separation processes are commonly applied to separate a liquid under a pressuregradient through a semi-permeable membrane into two liquid streams of different composition,the permeate (which flows through the membrane) and the retentate (which concentrates thosesubstances which do not pass through the membrane in a reduced volume of fluid). Theseprocesses are applied in dairy processing for an ever-increasing range of applications, e.g.concentration, demineralization, protein separation, or removal of bacteria.9.2 UltrafiltrationUltrafiltration (UF) enables concentration of casein content and recovery of whey proteins forcheese manufacture. UF of milk at pH 6.66.8 concentrates mineral salts bound to casein micellesin the same proportion as proteins and increases buffering capacity, which affects acidification,pH, rennet coagulation and rheological characteristics of curd. Acidification before or during UFand/or salt addition to retentate leads to solubilisation of colloidal calcium in the permeate.As a result of UF of milk, globular fat, caseins, whey proteins and micellar salts, are selectivelyconcentrated in the UF retentate, whereas lactose, serum salts and peptides, are found largely inthe UF permeate at their original concentration. This has two major implications for cheesemaking properties of milk:(1) The inter-micellar mean free distance is reduced considerably, thereby forcing the micell es tointeract more frequently with each other as a result of collisions induced by Brownian motion.(2) The buffering capacity of the milk is increased considerably due to the increasedconcentrations of proteins and micellar minerals in the UF retentate, both of which are keycontributors to the buffering capacity of milk, particularly in the pH region 5.57.0.As a result of these changes, the cheese making properties of UF retentates differ from those ofunconcentrated milk in several aspects. RCT decreases and firmness increases when cheese milk ispartially supplemented with UF retentate. Cheese made from UF retentate is often characterizedby a long time required to reach the desired pH and an acidic taste which is related to the higherbuffering capacity of a UF retentate. Furthermore, flavour development in hard and semi-hardcheese made from UF retentate is generally slow, which has been related to a reduced rate ofproteolysis of caseins during ripening of such cheese, probably resulting from re tention ofinhibitors of chymosin and plasmin in the UF retentate.9.3 MicrofiltrationMicrofiltration (MF) may be used for partial microbial decontamination of cheese -milk andstandardization of the casein content of milk, rather than the total protein content that isstandardized by UF. Cheese prepared from microfiltered milk may lack flavour development due39

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to absence of flavour producing organisms during ripening as they are filtered out in permeateduring MF. MF uses larger pore sizes and lower pressures than UF. Whey proteins are smallermolecules (3 to 5 m) compared to casein micelles (15 to 600 nm) and can be separated by use of0.1 to 0.2 m pore size membranes. This separation produce casein-enriched retentate andpermeate containing significant amounts of native state -lactalbumin and -lactoglobulin.Casein-enriched milk prepared by MF has been reported to have improved rennet coagulationproperties and reduced loss of fat and fines in the whey. Increasing MF concentration factor resultin increased moisture, protein and calcium contents, total solids recovery, actual and compositionadjusted cheese yields, proteolysis and flavour and decreased hardness.9.4 Standardization of Cheese-Milk by Protein AdditionStandardization of milk protein/casein levels may be used to reduce some negative defectsassociated with a seasonal milk supply such as variable protein/casein contents which result inpoor curd-forming properties and in variations in yield and in composition and consistency ofresultant cheeses. Increased yield results from reduced losses of fat and casein particles in wheyand better retention of whey proteins in the aqueous phase of cheese. Furthermore,standardisation of milk protein to higher than normal levels enables increased plant throughputwithout installation of extra cheese vats. Protein standardization may be achieved by: use of lowconcentrated retentate (LCR) produced by UF or Reverse Osmosis (RO) of cheesemilk; enrichmentof casein by MF; or addition of phosphocasein powder (PC) or milk protein concentrate (MPC),typically followed by cheese manufacture using conventional equipment. Standardization ofcheese is normally done to a casein/fat ratio of 0.70:1.0.

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Lesson 10HEAT TREATMENT AND HOMOGENIZATION OF CHEESE MILK10.1 IntroductionMost cheese-making today involves the treatment of milk by one or more processing steps prior toaddition of coagulant and starter culture. Perhaps the simplest and earliest technologicalintervention, driven by safety concerns, was the pasteurization of milk. Pasteurisation inactivatessome enzymes, reverses shifts in the mineral balance of milk and influences the microflora of nonstarter lactic acid bacteria (NSLAB) in the final cheese. Pasteurization unacceptably impairs thecheese flavor as a result of its influence on NSLAB. On the other hand, more severe heattreatments than pasteurization result in significant denaturation of whey proteins and theirresulting incorporation into cheese curd, with significant effects on cheese yield and composition.10.2 Heat TreatmentsMilk for cheese manufacture is heated to eliminate pathogenic bacteria, to minimise damage tocaseins by proteolytic bacteria on storage or to incorporate heat-denatured whey proteins in curd,thereby improving cheese yield. Furthermore, more severe heat treatment of milk may be appliedto inactivate spores from Clostridium tyrobutyricum. Heat treatment of milk at conditions severethan those used for conventional pasteurisation results in denaturation of whey proteins,interactions between whey proteins and casein micelles and transfer of soluble calcium,magnesium and phosphate to the insoluble colloidal state. Casein micelles are very stable at hightemperatures, although changes in zeta potential, size, hydration of micelles and some associationdissociation reactions do occur under severe heat treatments. Denaturation of whey proteinsexposes side chain groups originally buried in the native structure, particularly reactive thiolgroups, and the unfolded proteins may self-aggregate or interact with casein micelles, throughinteractions with -casein. The extent of association of denatured whey protein with caseinmicelles is dependent on the pH of the milk prior to heating, levels of soluble calcium andphosphate, milk solids concentration and mode of heating (direct or indirect). For cheese-makers,the principal interest has been in increasing yield by exploiting this heat-induced association ofcaseins with whey proteins, while attempting to minimise undesirable changes in cheese quality.In the cheese vat, high heat treatment of milk prolongs rennet coagulation times and reduces thestrength of rennet gels leading to impaired syneresis. The adverse effects on coagulation areattributed to the inhibition of hydrolysis of -casein by chymosin due to the -lactoglobulin/casein complex at the micelle surface impairing the accessibility of -casein to the coagulant, toreduced reactivity of renneted micelles with attached denatured whey proteins to aggregation, orto a reduction in the concentration of micellar calcium.10.3 Homogenization of Cheese-MilkThe primary aim of homogenization of milk is to reduce the size of the fat globules, therebydelaying their creaming rate. In raw milk, fat globule size commonly ranges from 0.215 m, and41

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homogenization generally aims to reduce the maximum to < 2 m. For this purpose, two -stagevalve homogenizers are used, which operate at pressure of 20 MPa. Recently, novelhomogenization devices, e.g. high-pressure homogenizers and microfluidisers, which can operateat pressures of several hundred MPa and achieve greater reductions in fat globule size, have beendeveloped. In cheese making, homogenization of cheese milk can be of interest for preventingcreaming of fat globules, reducing fat losses in the whey or controlling development of free fat inthe cheese. Due to the reduction in fat globule size on homogenization, the total surface area of thefat globules increases and the amount of original fat globule membrane material is by farinsufficient to fully cover the newly-formed surface. As a result, other surface-active componentsof milk, primarily caseins and, to a lesser extent, whey proteins, become adsorbed onto the surfaceof the newly formed globules. Thus fat globules in homogenized milk almost resemble caseincovered emulsion droplets. The adsorption of caseins onto the fat globules has the followingimplications for cheese-making characteristics of milk:(1) Casein surface area in milk is increased, but the amount of micellar casein is reduced ;(2) Two types of particles with a casein micelle surface layer exist: native casein micelles andcasein-covered fat globules;(3) When adsorbed, casein micelles tend to spread over the surface of the fat globule and henceincrease in effective surface area but with reduced surface density of -casein.The rennet coagulation time (RCT) of unhomogenised milk is generally lower than that ofhomogenized milk. This is probably related to the larger casein surface area in homogenized milk,as well as the lower surface density of -casein. The former increases the probability ofinteractions between particles, whereas the latter reduces the amount of -casein that needs to behydrolyzed before micellar flocculation is induced. Negative aspects of homogenizatio n occur inthe subsequent stages of cheese making, i.e., the syneresis of the paracasein matrix and the fusionof the paracasein micelles into a strong and cohesive network. Cheese curd from homogenizedmilk shows poor syneresis and, as a result, has high moisture content. Furthermore, cheese curdprepared from homogenized milk is also often characterized by a coarse and brittle structure.10.4 High-Pressure Treatment of Cheese milkCheese prepared from raw milk is better than the cheese manufactured from pasteurized milk butfor safety reasons, pasteurization of milk before cheese making is essential. High pressuretreatment (HPT) of milk can be used as an alternative to pasteurization so that raw milk qualitycheese can be produced without compromising safety aspects. High pressure treatment is a nonthermal process wherein a high pressure in the range of 200 to 1000 MPa for different time periodsis used for destruction of microorganisms.HPT of milk causes several protein modifications such as whey protein denaturation and micellefragmentation and alters mineral equilibrium. These changes improve rennet coagulation ofcheese milk and yield of cheese. HPT of milk results in smaller casein micelles due to which RCTdecreases. Cheese yield increases owing to denaturation of whey proteins by HPT (resulting intheir incorporation in cheese curd), which also leads to increased moisture retention.

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Module 5. Cheese additives

Lesson 11CHEESE ADDITIVES AND PRESERVATIVES11.1 IntroductionIn addition to certain major processing aids such as starter bacteria, internal and external moldsand coagulants, various additives used in the manufacture of cheese serve as manufacturing aids.Some of them also prevent fermentation faults (e.g. late blowing).11.2 Salts to Restore the Calcium Balance in MilkCalcium in milk is present as soluble, colloidal and complexed forms in a very delicate bala nce.Successful coagulation depends on this balance of calcium. Sometimes the balance among thethree different forms is disturbed due to heat treatment, cooling or disturbances in milk itself(colostrum, late lactation, mastitis). In such cases it has become a common practice to add calciumsalt, usually calcium chloride, to milk. This is especially necessary when some of the vegetable ormicrobial coagulants are used. Other calcium salts which can be added include calcium lactateand calcium hydroxide. They are in the form of a solution. Bovine milk contains 0.123% calciumwhile maximum clotting advantage occurs at a concentration of 0.142%. Therefore, addition of0.02% calcium chloride is suggested. If excess is added, s casein- casein complex dissociates andthe s casein no longer has the protection from the casein and a precipitate forms. Slightly lesscalcium chloride will produce a harsh inflexible curd. Rarely is more than 0.02% of calciumchloride needed for satisfactory coagulation even when using highly heated milks. Retention oftoo much calcium chloride, apart from producing a hard unyielding curd, produces a cheesewhich is bitter in flavor and with a harsh body.11.3 Salts Inhibitory to Undesirable OrganismsSalts like potassium nitrate, sodium hydrogen carbonate, calcium carbonate, mono -sodiumdihydrogen phosphate and nisin are added to arrest the growth of undesired microorganisms.These are commonly added in some of the less acid curd cheese like Edam, Gouda etc. mainly toprevent the growth of gas producing organisms which cause blown defe ct in cheese. Nitrate incombination with salt has been used to control the gas forming butyric acid bacteria and at thesame time, it does not have any affect on the growth of lactic and propionic acid bacteria. But theuse of nitrates in cheese is limited due to two main reasons:1. Certain amino acids react with nitrite to produce color defects2. Production of nitrosamines which are carcinogenicNisin may be used in processed cheese to inhibit the activity of gas producing organisms but notin natural cheese, because the bacteria present in natural cheese destroy the activity of nisin.

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Sorbic acid is used to inhibit the growth of yeasts, molds and some bacteria. However, its activityagainst bacteria is not as comprehensive as that against yeasts and molds.11.4 Use of Common Salt (NaCl)Salt normally used in cheese making is about 2% of the weight of the curd. Salt is added to cheese:a. To suppress growth of unwanted micro-organisms,b. To assist the physico-chemical changes in the curd,c. To slow down the growth of the lactic acid and other types of unwanted microorganisms,d. To give the cheese an appetizing taste.SpecificationCommon salt contains 99.6% NaCl on moisture-free basis limits are given for alkalinity (0.03%Na2 CO3 ), insoluble matter (0.03%), sulfide (0.3% Na2 SO4 ), iron (0.001%), copper (0.002%), arsenic(0.0001%), lead (0.0005%), calcium (0.1%), and magnesium (0.01%) dried salts should passcompletely through an 18-mesh sieve.Effect of quality of salt on cheese:1) Use of impure salts results in faulty color in presence of iron, copper and lead. The fault couldbe avoided by acidifying the brine to pH 5.0 with lactic acid.2) Fine salts may increase the rate of loss of whey and thus protein and fat from the curd.Effect of quantity of salts on cheese:1) Exert an appreciable effect on growth of molds in blue veined cheese.2) Low concentration stimulates most microorganisms and some enzymes.11.5 AcidulantsThe most common acidulant used in cheese making is lactic acid, which is produced in situ bylactic acid bacteria present naturally in milk. Pure defined cultures of lactic acid bacteria (LAB) canalso be used. However, the use of acids for chemically acidifying the milk is also practised. Acidsof food grade quality (e.g. lactic, glacial acetic, lemon juice, vinegar, D-glucono-delta-lactone,phosphoric) are used to increase the acidity of milk. Glacial acetic acid (12.5% concentrated acid @ 2.7% of milk) is used in Queso Blanco cheese andvinegar (0.03%) for mozzarella cheese manufacture. Lime juice is used in India to manufacture Bandal cheese, paneer and channa. D-glucono-delta-lactone when heated produces acid and it has been used for the production ofacid in milk and curd. The cheese made by using this acidulant is bland and lacks flavor as noenzymes are formed in this process.44

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Phosphoric acid (10% strength) is diluted @ 4 l in 40 l of water and then added to 1000 l of milkwith vigorous stirring.11.6 Colors and Bleaching AgentsThe color of the product is an important factor in the consumer appeal of the product. It is acommon practice to add extra color to pale colored milk to give cheese an attractive andappetizing appearance. The colors of importance in milk are riboflavin and carotenoids.Riboflavin is yellow in solution with a green-yellow fluorescence and tends to give curd agreenish tinge. However, most of this color is lost in whey as riboflavin is water soluble.Therefore, its effect as color in cheese is small. The deep yellow orange color due to carotenoids ismore significant. As there is a large seasonal variation in color of milk, colors are added to obtainuniform color in cheese. Annato is, by far the most widely used color. It is extracted from seeds ofa plant Bixa orellana in sodium hydroxide. The pigment in annatto is the acid bixin which, in thealkaline extract becomes norbixin. The color is composed of tints of yellow and red units, and incheese, becomes a protein dye attached to the casein. Annatto is very susceptible to oxidation.Agents such as H2O2 , air, -SH groups in ripening cheese and copper and iron act as catalysts inoxidation of annatto pigment. Thus, bleaching of the red color in patches in cheese is frequentlyfound in poor quality, moist or contaminated curd.Sometime it becomes desirable to bleach the color to meet the market demand particularly intraditional products. For example the customers expect Mozzarella cheese to be white as it is madefrom buffalo milk. In case cow milk has been used, it will yield a yel low product. In such casesbleaching agents may be added to milk. Benzoyl peroxide, H 2 O2 and other color masking agentsare used for this purpose.11.7 Flavors, Spices and HerbsThere are two groups of flavoring agents which are added to cheese: (a) those which are added forimparting flavor to the cheese (herbs and spices), and (b) those flavors which are nutritive foods intheir own right (ham, meats etc.), which are enclosed in the cheese which serves simply as a softenclosing base.Chopped herbs, or their juices, or dried crust semi powders have been used to impart flavor andaroma in cheese curds. The herbal mixes are incorporated in the raw cheese at moulding timebefore pressing, or are mixed with partially or wholly ripe curds pressed into shapes orcontainers. Spices which have been used include aniseed, caraway seed, cloves, cumin, cinnamon,ginger, nutmeg, pepper etc. Herbs used in cheese include mint, sage, lavender, chives etc.11.8 SmokesCertain cheeses are exposed to a smoke-charged atmosphere for smoky flavor development. Itcauses fat to melt and come out the surface of the cheese block, and no moisture to evaporate.Incorporation of smoke vapors containing phenolic substances has preservative effect and alsoimpart typical flavor to cheese. Sometimes cheese is dipped in liquid condensed smoke.11.9 Addition of BeverageAlcoholic beverages, beers, wines and liquors have been added to the raw cheese curd oralternatively, the whole cheese has been immersed in the liquid. The mixing of flavors, vegetables,

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spices, meat, etc. seems to break with tradition to satisfy the taste of modern society particularlyfor snack foods.11.10 Cheese BasesThe use of a bland cheese base along with a filling of herbs, vegetables and chopped cooked meatsis probably a spillover from the use of processed cheese in the similar manner. The typicalmixtures use cheese as a base, with the addition of lettuce, chives, onions, spinach, potatoes,carrots, chopped ham etc.

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Module 6. Role of starter culture in cheese making

Lesson 12STARTER CULTURES12.1 IntroductionThe use of starter cultures is an essential requirement in the manufacture of most cheeses. Acheese starter may be defined as a milk culture containing selected lactic acid bacteria,usually Lactococcus lactis subsp. lactis, Lc. lactis subsp. cremoris, Lc. lactis subsp.diacetylactis, whichconvert about 1% (absolute) of lactose in milk almost entirely to lactic acid, along with very littleamounts of byproducts such as acetic acid and carbon dioxide. Acid production at an appropriaterate and time are the key steps in the manufacture of good quality cheese.Milk sours on storage, but if the milk is heated, the souring is delayed because the acid-producingbacteria present in milk are destroyed by heat treatment. The course of deterioration then becomesnot a clean, wholesome souring, but a change which may include souring but also often producestaints, protein and fat break down and sometimes even putrefaction. It is, therefore, essential to reinoculate heated milk with acid producing organisms if clean, sour milk is desired. Starter culturesare intentionally added to cheese milk to initiate and accomplish the desired fe rmentation. Itensures consistent souring at a controllable rate, gives desired clean lactic flavor and helps tosuppress any tendency for taint-producing microorganisms to grow in milk. Acid productionaffects several aspects of cheese manufacture, e.g.1. Denaturation and retention of the coagulant in the curd during manufacture and hence the levelof residual coagulant in the curd. This influences the rate of proteolysis during ripening and mayaffect cheese quality.2. Curd strength, which influences yield.3. Extent of dissolution of colloidal calcium-phosphate.4. Gel syneresis, which controls cheese moisture and hence regulates the growth of bacteria in thecheese. Consequently it strongly influences the rate and pattern of ripening and the cheese quality.Acid production, combined with milk heating and stirring of curd-whey mixture causes the caseincurd to shrink and expel moisture from the coagulum.5. The rate of pH decrease determines the extent of dissolution of colloidal calcium phosphatewhich modifies the susceptibility of the caseins to proteolysis during manufacture and influencesthe rheological properties of cheese, e.g. textural differences among Emmental, Gouda, Cheddarand Cheshire cheeses.6. Acidification controls the growth of many species of non-starter bacteria in cheese, especiallypathogenic, food poisoning and gas producing microorganisms. In addition to producing acid,many starter bacteria produce probiotics which also restrict or inhibit the growth of non-startermicroorganisms.47

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7. Starter organisms govern flavors and body and texture of cheese.

8. Acid production influences favorably the changes that take place in the curd during cheddaring.9. Growth of LAB produces the low oxidation-reduction potential (Eh) necessary for production ofreduced sulphur compounds such as methanethiol which may contribute to the aroma of Cheddarcheese.12.2 Requirements of a Good Starter

It must be vigorous, and produce acid at a quick, consistent and controlled rate.

It must produce a clean lactic acid flavor and other aroma.

Must not produce any off flavor, taint, pigment or gas. There must be no appreciableproteolysis or lipolysis.

Must contain only lactic acid bacteria of desired type.

It must produce acidity smoothly under the conditions of manufacture.

12.3 Type of Cultures

Essentially two types of starter cultures are used: Mesophillic milk an optimum temperature of~30C and thermophillic milk an optimum temperature of ~45C. The choice of culture dependson the cheese being made, e.g. mesophillic cultures are used in the production of Cheddar, Gouda,Edam, Blue and Camembert while thermophillic cultures are used for Swiss and Italian varieties(Table 12.1). This choice is related to the method of manufacture since Swiss and Italian cheesesare cooked at much higher temperature (50-55C) which the starter bacteria must be capable ofwithstanding. Growth at 10 and 45C can be used to distinguish mesophillic from thermophilliccultures while microscopic observations, measurement of the amount and isomer of lactic acidproduced and the ability to metabolize citrate can readily distinguish most of the species withinthese broad categories. Both mesophillic and thermophillic cultures can be further subdivided intomixed (undefined) cultures, in which the number of strains is unknown and defined cultures inwhich the member of strains is known.Table 12.1 Starter cultures used in major cheese varieties

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12.3.1 Mixed strain mesophillic cultures

Undefined or mixed-strain mesophillic cultures are composed mainly of Lc. lactis subsp. cremoris,although occasionally they also contain the closely related Lc. lactis subsp. lactis. Some mesophillicmixed cultures also contain a lactococcus (Lc. lactis subsp.diacetylactis) which metabolizes citrate(Cit+) to CO 2 and flavor compounds. Thus, many mesophillic cultures are comprised of Cit andCit+ lactococci. Depending on the nature of the flavor producers, mesophillic mixed cultures areclassified as: L-type, containing leucouostoc spp; D- type, containing Cit+ lactococci (diacetylactis),DL- type containing both, and O-type containing no flavor producers. The flavor producers usecitrate as energy source. The acid and flavor producers in mesophillic cultures comprise about90% and 10% of the microflora respectively. They are called mixed cultures not only because theycontain different bacterial species but also because they contain different strains of the samespecies.Mixed starters consist of two or more strains or species and so may be more variable in behavior.These are safer to use because if one strain becomes phaged, others can usually continue to work.However, it is difficult to maintain a constant mixed starter because one strain becomes dominantafter a few transfers. Therefore, each strain should be cultured separately, and mixed immediatelybefore addition to the vat.12.3.2 Defined strain mesophillic culturesThese are mainly pure cultures of Lc. lactis subsp. cremoris. The important differences betweenthese cultures and traditional mixed cultures are that the number of strains is known and they donot contain flavor producers.Single strain starter is a pure culture usually consisting of either Lc. lactis subsp. lactis or Lc.lactis subsp. cremoris. This type of culture has the advantage that if found satisfactory in vigor andflavor, it can give a steady acid production and thereby a predictable quality fermented dairyproduct. However, there is serious disadvantage as well with this type of starter. During itsapplication, if it gets attacked by phage or fails by any other reason the quality of the product canbe adversely affected.Other bacterial species are sometimes incorporated into a dairy starter cultures and these are asfollows:1. S. faecium: for manufacture of modified Cheddar cheese.2. Brevibacterium linens: Imparts distinctive, reddish orange color to the rind of Brick andLimburger cheese.3. Propionibacterium freudenreichii subsp. shermanii, for Swiss cheese; produces large gas holes incheese.Molds like Penicillium camemberti, P. caseiocolum and P. candidum and the blue mold P. roquefortii,which grows internally in the cheese are used in Blue cheeses like Roquefort, Blue stilton, Danishblue, Gorgonzola and Mycella.Most cultures are used in dairy industry either singly, in pairs or in a mixture, thus, giving theindustry the opportunity to manufacture different types of fermented dairy products. In theory, a49

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single strain starter consists of one type of organism but in practice, it is rarely used. However,single strains can be paired to safeguard against bacteriophage attack, intolerance of salt, o rcooking temperature and variation in the quality of the product. Multiple strain starter culturesconsist of known member of single strains, so that the starter can be used for an extended periodof time during cheese making season. A mixed strain starter is a combination of Lc.lactis subsp.lactis, Lc. lactis subsp. cremoris and the gas and aroma producing mesophillic LAB (Lc.lactis subsp. diacetylactis, Lc. lactis subsp.cremoris and/or Leuc. dextranicum).12.4 Factors Affecting Activity of Starter Culture Temperature pH Strain compatibility Growth medium inhibitors Bacteriophage Incubation period Heat treatment of milk Degree of aeration (aeration, agitation and surface culture not favorable) CO2 (minimum concentration is essential) Storage conditions12.5 Desired CharacteristicsGood starter should show a smooth curd. At the completion of the incubation, there should be noseparation of the whey from the curd. After the cooled starter has been stirred or shaken, it shoul dhave the consistency of rich cream. It should be glossy in appearance and not dull or chalky. Thestarter should show no curd particles or lumps, and when poured from the container it should notshow a ropy consistency. The flavor should be pronounced, yet delicate. Neither a flat flavor nor asharp acid taste is desired.

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Lesson 13PROBLEMS ASSOCIATED WITH CHEESE STARTERS13.1 IntroductionStarter trouble has been known since the beginning of cheese technology, but it has only becomeacute since pasteurization of milk has been practiced for cheese making. This is not becausepasteurization weakens the milk, but because bulk raw milk is a starter itself; some lactococciwill always grow and sour the milk. In pasteurized milk, if for any reason the starter fails, thereare too few lactococci left in the milk to permit souring. As already emphasized in the previouslesson, a good starter must produce lactic acid at a vigorous and steady rate. When it no longerdoes so, the starter is said to be slow or defective.13.2 Defects in StarterSharp acid taste: It is due to over-incubation (due to higher temperature and longer time) of milkand increased rate of inoculum.Bitter taste: This may come from milk.Cheesy flavor: This may be due to growth of undesirable bacteria.Flat flavor: This is caused by less citrate in milk, less number of citrate fermenting organisms orunfavorable incubation conditions for the growth of citrate fermenting organisms.Uncoagulated starter: This is due to too low/high incubation temperature of starter or pooractivity of mother culture or due to the presence of bacteriophage and antibiotics.Gassiness: This is due to improperly pasteurized milk, post-pasteurization contamination of milk,unsterilized transfer equipment and/or contaminated mother culture.13.3 BacteriophagePhages are viruses or ultra-microscopic organisms, specifically parasitic on bacteria.Bacteriophage causes lysis or destruction of bacteria and can be transmitted from one culture toanother. Lysis of bacteria by phages involves the attachment of the phage particles to the cell wall,which is then digested to permit entry and multiplication of the phage in the bacteria.Preventive measures against phage attack:

There are two sterilization methods of combating phage in cheese premises: the use of heator chemicals. Neither method is fully effective unless the plant surfaces and equipment arethoroughly clean.

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Contamination by droplets of moisture containing phage should be avoided in the vicinity

of cheese or starter rooms (curd and whey separation).

Cracked floors should be repaired.

Hypochlorite solution should be sprayed/applied on the interfaces of the equipment (20 -50ppm for overnight or 200-300 ppm for immediate use of the equipment).

Starter cultures should be used in rotation.

Phage-resistant and/or mixed-strain starters can be used.

13.4 Causes of Slow Starters

1. Spontaneous loss of viability inherent in the starter culture.2. Incompetence in the handling of starter

Allowing contamination

Too infrequent sub-culturing

Use of unsuitable media

Culturing at inappropriate temperature.

3. Inhibitory causes in the milk itself

Abnormal milk

Silage milk

Seasonal factors

Conditions in milk adverse to the growth of organism e.g. changes in chemical

composition

Inhibitory bacteria in milk

Inhibitory substances in milk

Excessive leucocytes

Presence of antibiotics

Presence of preservatives

4. Deviation from standard cheese making procedure

5. Bacteriophage action52

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13.5 Causes of Starter Failures

13.5.1 Intrinsic factorsa) Physiological starter: LAB produces lactic acid at the rate of 10% of their weight. This rapidproduction of acid, though advantageous in the manufacture, is a marked disadvantage to cultureitself.b) Genetic instability: LAB spontaneously produces mutants which are unable to utilize lactoseand become deficient in protease activity. Consequently, they do not grow properly in milk.13.5.2 Extrinsic factorsa) Variations in processing conditions e.g. temperature, salting rate, etc.b) Variations in milk composition e.g. due to mastitis, mineral content, period of lactation, etc.c) Variations in levels of natural and added inhibitors e.g. bacteriophage, antibiotics, detergentsand sanitizers etc.d) Mastitis:

Changes the chemical composition of milk: decrease in lactose, casein, calcium and acidity

Changes concentrations of some enzymes, vitamins and bacterial growth factors

Increases the number of bacteria

Produces substances toxic to starter organisms

e) Colostrum - Milk drawn up to 24 h after calving does not promote growth.

f) Late lactation - Changes the chemical composition of milk in terms of decreased lactose andincreased chlorides.g) Excessive aeration - LAB grow and multiply on energy derived from the breakdown of milksugars. This is an anaerobic process. Also, some bacteria are provided with a mechanism whichcan convert the oxygen of the air to H2O2 which in turn is strongly toxic to LAB. Aeration reducesthe CO 2 which stimulates growth of many contaminants.h) Inhibitory bacteria: A large member of microorganisms can produce chemical substances whichare inhibitory.13. 6 Natural Inhibitory Substances in Milk13.6.1 Antibiotics in milkWidespread use of penicillin and other antibiotics may lead to the animals, under treatment,excreting antibiotics in their milk to be a cause of starter inactivity. Antibiotics may also be

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produced by the starter organisms themselves, by one or more strains in a mixed starter culture orby contaminating microorganisms.13.6.2 Inhibitions by rancid milkRaw milk rapidly turns rancid, unless cooled quickly because of the presence of an abnormalconcentration of lipase. Such rancid milk may be inhibitory to LAB and other microorganisms.Fatty acids (C8 -C12 ) exert specific effect on the growth of microorganisms.13.6.3 LacteninsLactenins (L1 and L2) are present as natural inhibitory substances in milk. They are inactive underanaerobic conditions and in the presence of -SH compounds. The presence of both fractions isnecessary for maximum inhibition, and even then the effect is bacteriostatic rather thanbactericidal. Lactenins are destroyed by heating at 74C/20 min.

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Module 7. Rennet preparation and properties

Lesson 14CALF RENNET: PREPARATION AND PROPERTIES14.1 IntroductionRennet is a complex of enzymes produced in any mammalian stomach to digest the mother's milk.Rennet contains many enzymes, including a proteolytic enzyme (protease) that coagulates themilk, causing it to separate into curd and whey. The active enzyme in rennet is called chymosin orrennin but there are also other important enzymes in it, e.g. pepsin and lipase. There are nonanimal sources for rennet also that are suitable for vegetarian consumption.Natural calf rennet is extracted from the inner mucosa of the fourth stomach chamber (theabomasum) of young, unweaned calves. If rennet is extracted from older calves (grass-fed orgrain-fed) the rennet contains less or no chymosin but a high level of pepsin and can only be usedfor special types of milk and cheeses. As each ruminant produces a special kind of rennet to digestthe milk of its own species, there are milk-specific rennets available, such as kid goat rennet forgoat's milk and lamb rennet for sheep's milk.14.2 Enzymes in RennetRennin is an enzyme which can function very powerfully as a clotting agent at pH 6.2 to 6.4. Theterm chymosin is used in place of rennin to avoid confusion with another enzyme renin, whichcan be extracted from the kidney. The ratio of clotting to proteolytic power of chymosin/rennin isvery high. Conversely, the other enzyme pepsin, functions best at high acidities (pH 1.7-2.3) andthe ratio of clotting to proteolytic power is lower. All proteolytic enzymes can clot milk but thespecific value of rennet in cheese making is that it gives rapid clotting without much proteolysis.Proteolysis by enzymes like pepsin, papain etc. can lead to bitterness in cheese.The rennet extract from the young milk-fed calf contains 88-94% rennin and from 6-12% pepsin,while in extracts from the older fodder eating bovine, it is almost reverse i.e. 90-94% pepsin andonly 6-10% rennin. So, there is variable amount of pepsin in rennets depending on the age andfood of the calf from which the rennet is obtained.14.3 Preparation of Rennet14.3.1 Traditional methodDried and cleaned stomachs of young calves are sliced into small pieces and then put intosaltwater or whey, together with some vinegar or wine to lower the pH of the solution. After sometime (overnight or several days), the solution is filtered. The crude rennet that remains in thefiltered solution can then be used to coagulate milk. The enzyme present at this stage is calledprorennin which on acidification, becomes rennin with an increased clotting ability. About one55

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gram of this solution can normally coagulate 2 to 4 litres of milk. This method is still used by sometraditional cheese-makers, e.g. in Switzerland, France, Romania, Italy, Sweden, United Kingdomand Alp-Sennereien in Austria.14.3.2 Modern methodThe commercial enzyme is prepared from the fourth stomach (abomasums) of the calf, known asthe vell. The lining of the stomach is washed, dried, cut into small pieces and macerated in watercontaining about 4% boric acid at 30C for about 5 days. Alternately, a brine extract at 15-20C canbe prepared. A common method is to dry the vells by inflation and afterwards cut them into stripsand extract with sodium chloride solution (up to10%) for few days. Crude rennet extract containsactive rennin as well as inactive precursor (prorennin). Addition of acid to the extract facilitatesconversion of the prorennin to rennin and allows the extract to reach maximum activity. Finally,the activated rennet is standardized with respect to activity, salt concentration, pH and colour.Liquid rennet is usually preserved by a high salt content (14-20%) and by the addition ofpreservatives such as sodium benzoate and propylene glycol. Rennet powders are prepared fromprecipitates obtained by acidifying activated extracts or by saturating with sodium chloride, orboth.In one kg of rennet extract, there are about 0.7 g of active enzymes. The rest is water and salt andsodium benzoate. Typically, one kg of cheese contains about 0.0003 g of rennet enzymes.14.4 Properties of RenninRennin is a sulphur-containing protein. One part can clot about 50, 00,000 parts of milk. It is easilydestroyed by heat, many chemical substances and many physical conditions. The isoelectric pointof rennin is about 4.55 and it is easily destroyed by factors such as heat and high pressures. It isalso digested by proteolytic enzymes and is readily adsorbed. It is very sensitive to alkali, andheating at 70C at pH 6.8-7.0 will destroy it in 14 min.Optimum pH for clotting of milk is 5.4 and the proteolytic power of this enzyme virtuallydisappears at pH 4.5.

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Lesson 15RENNET SUBSTITUTES15.1 IntroductionMilk coagulation is a basic step in cheese manufacturing. Calf rennet, the conventional milkclotting enzyme obtained from the fourth stomach of suckling calves was the most widely usedcoagulant in cheese making all over the world to manufacture most of the cheese varieties. Theworldwide reduced supply of calf rennet and the increase in cheese production and consumptionhave stimulated research for milk-clotting enzymes from alternative sources to be used as calfrennet substitutes. Further, if calf rennet is used as a coagulant for cheese making, the product hasto carry a tag of non-vegetarian which may lead to non-consumption of cheese by vegetarianpopulation of the world. Thus, it was found necessary to discover milk clotting enzymes fromalternative sources.15.2 Desirable Characteristics of Rennet SubstitutesOther than fulfilling the legal requirements, rennet substitute from any alternative source shouldpossess the following characteristics: The ratio of milk clotting activity to proteolytic activity should be high. This means that the milkshould clot without much proteolysis i.e. breakdown of proteins to peptides. This preventsexcessive nonspecific proteolysis during manufacture and hence protects against a weak gelstructure, high losses of protein and fat in the whey, and reduced yields of cheese solids.Moreover, it avoids excessive proteolysis during maturation and thus ensures the correct balanceof peptides of different molecular weights and hence desirable flavor, body, and functionalcharacteristics in the ripened cheese. It should be thermally stable (comparable to calf rennet) at pH and temperatures used duringcheese making. This influences the level of residual rennet in cheese and hence influences thebiochemical changes that take place during ripening. It should have low thermal stability at temperatures of whey processing otherwise it may hinderthe utilization of cheese whey in various products. It should impart desired flavor, body, and texture characteristics to the finished cheese.15.3 Milk-clotting Enzymes from PlantsEnzymes from many plant sources may be used as clotting enzymes in cheese making but most ofthe plant proteases are strongly proteolytic and cause extensive digestion of the curd, resulting inreduced yields, bitter flavors and pasty-bodied cheese.

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15.3.1 PapainThe latex of the plant Carica papaya yields papain and several other proteases. It has powerfulmilk clotting activity but it is also highly proteolytic. It requires a free sulfhydryl group for itscatalytic activity.15.3.2 FicinFicin is present in the latex of several species of the genus Ficus (fig) such as Ficus glomarata, Ficusreligiosa and Ficus carica but the best source is Ficus carica. Cheese made with ficin develops bitterflavor which decreases in intensity during curing.15.3.3 OthersBromelain from pineapple has also been considered as a possible substitute for calf rennet. Anenzyme extracted from Withania coagulans was also used in the manufacture of Surati andCheddar cheese. Extracts from the flower petals of Cynara cardunculuswere used for themanufacture of Serra cheese from sheeps milk by Portuguese farmers.15.4 Microbial RennetA large number of microorganisms are known to produce milk clotting enzymes. The possibilityof a few of the microorganisms proving successful as rennet substitutes may appear from the factthat they play an important part during the manufacture of cheese. Microbial enzymes are knownto exhibit considerable variations in the range of activity, substrate specificity and mode of action.Even more important is the fact that they can be produced economically on any desired scale.Many hundreds of bacterial and fungal cultures have been investigated for milk clotting enzymesand their proteolytic abilities. Milk clotting enzymes from bacteria like Streptococcus liquefaciens,Micrococcus caseolyticus, Bacillus cereus, B. polymyxa, B. mesentericus, B. coagulans and B. subtilis havebeen used as coagulating enzymes. Milk clotting enzymes from fungi are also used during cheesemaking. Some of the fungi producing such enzymes are Aspergillus nidulans, A. galucus,Syncephalastrum racemosum, and Cladosporium herbarum. Some of the microorganisms used incommercial production of microbial rennet are listed in Table 15.1.Table 15.1 Micoorganisms used in commercial production of microbial rennet

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Various strains of these organisms behave differently; therefore, the cheesemaker should use onlywell tried and tested rennet for the types of cheese contemplated. The activity of various microbialrennets varies according to pH and enzyme system.The protease of the Mucor miehei coagulants degrade casein fairly rapidly in the pH range 5.5-7.0;but inspite of this, the incidence of bitter cheese using this enzyme is low. The enzyme is verysensitive to temperatures in the region 37-45C and is destroyed at 70C. This enzyme is usedsuccessfully for many types of cheese.Mucor pusillus extract is also used as microbial rennet. It is highly proteolytic than calf rennet orthe Mucor miehei extract. An increase in calcium ion concentration in milk decreases the clottingtime but activity of this enzyme is not so pH-dependent as for other coagulants. It tends to givehard curds because of its high proteolytic activity and the curd tends to lose fat into the whey,thereby giving lower yield as compared to others. Thus, this enzyme is usually used incombination with other enzymes.The enzyme extracted from Endothia parasitica is more caseolytic than those from Mucor sp. or calfrennet and tends to produce more bitter flavors in high moisture cheese.Continuous research is being carried out in exploring the milk coagulating activity of enzymesfrom different cultures. Recently, commercial starter natto (Bacillus subtilis) has been studied forits milk clotting activity and it was found to be a potential rennet substitute.15.5 Recombinant ChymosinAs discussed earlier, many rennet substitutes are used for cheese making but many of theseproteolytic enzymes from microbial or plant origin cause flavor, texture and yield changes incertain types of cheese that are different than those produced by calf rennet. Further, they are notsuitable for long ripening cheeses as they have a different range of non-specific activities thanchymosin and do not produce the correct flavors on prolonged ripening.Recombinant rennet/chymosin can be prepared by gene transfer technology in which the bovinechymosin is cloned in a suitable production strain and the enzyme is produced by fermentation.This enzyme can be isolated and used in cheese making as a coagulant having properties similarto that of calf rennet. Escherichia coli, Kluyveromyces lactis and A. niger var. awamori have beensuccessfully used for production of calf rennet.In addition to the benet that such chymosin can be produced in large-scale fermentors at lowcost, recombinant and highly pure chymosin also has some other advantages such as specic, lowproteolytic activity, predictable coagulation behavior and vegetarian approval.With the advent of various sources of rennet substitutes, a number of firms are manufacturingthese substitutes at commercial level. Among these microbial rennet is most widely used.

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Lesson 16ACTION OF RENNET ON MILK16.1 IntroductionCasein and whey proteins are the two groups of proteins present in milk. Casein is mainly presentin micellar form and whey proteins are present in soluble form. When rennet is added in milk, theenzymes present in rennet act on the casein micelle leading to its destabilization and thuscoagulation takes place. So, to understand the basic chemistry behind this enzymatic coagulationof milk, it is important to understand the structure of casein and the forces that stabilize casein inmilk.The casein micelles are spherical colloidal particles, with a mean diameter of around 120 nm and amean particle mass of about 108 Da. The micelles contain protein and non-protein species (calciumand phosphate), with smaller amounts of magnesium and citrate and traces of other metals. Allthese are collectively called as colloidal calcium phosphate (CCP). The microstructure of caseinmicelle and its stability has been a subject of research for long. Numerous models have beenproposed such as sub-micelle model and dual-binding model. The sub-micelle model proposesthat the micelle is built up from sub-micelles which are held together by CCP and surrounded andstabilized by a surface layer rich in -casein but with some of the other caseins exposed also.Further, it was proposed that hydrophilic C-terminal region of -casein protrudes from thesurface, creating a hairy layer around the micelle and stabilizing it through a zeta potential ofabout -20 mV and steric stabilization. The dual-binding model of Horne proposes that individualcasein molecules interact via hydrophobic regions in their primary structures, leaving thehydrophilic regions free and with the hydrophilic C-terminal region of -casein protruding intothe aqueous phase.Calcium salts of s-casein and -casein are almost insoluble in water, while those of -casein arereadily soluble. Due to the dominating localization of -casein to the surface of the micelles, thesolubility of calcium -caseinate prevails over the insolubility of the other two caseins in themicelles, and the whole micelle is soluble as a colloid. Here calcium has the role to integrate thesub-micelles. If calcium leaves the micelle, the micelle will disintegrate into sub-micelles. Thestructure of the casein micelle is shown in figures 16.1 and 16.2.

Fig. 16.1 Casein Micelle Structure

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Fig 16.2 Structure of casein sub-micelle

16.2 Enzymatic Coagulation of Milk

The enzymatic coagulation of milk is essentially a two stage process (Fig. 16.3). As discussedearlier, the casein micelle is stabilized by -casein layer on the surface of the micelle. The enzymespresent in rennet (proteinases) hydrolyse -casein layer to form paracasein micelles whichaggregate in presence of calcium and thus milk is coagulated. The hydrolysis of the -casein layeris called as the primary phase of rennet coagulation while the aggregation of paracasein micellesin presence of calcium is called the secondary phase of rennet coagulation of milk.

Fig 16.3 Enzymatic hydrolysis of casein

The amino acid chain forming the -casein molecule consists of 169 amino acids. Rennet enzymesact specifically at 105 (phenyl alanine)-106 (methionine) bond of this amino acid, thereby splittingit into two parts. One part consists of amino acids from 1-105, called as para--casein. This part isinsoluble and remains in the curd together with s and -casein. The other part of amino acidsfrom 106-169 is soluble part. These amino acids are dominated by polar amino acids and thecarbohydrate, which gives this part its hydrophilic properties. This part of the -casein molecule iscalled the glycomacro-peptide and is released into the whey in cheese making.The formation of the curd is due to the sudden removal of the hydrophilic macropeptides and theimbalance in intermolecular forces caused thereby. Bonds between hydrophobic sites start todevelop and are enforced by calcium bonds which develop as the water molecules in the micellesstart to leave the structure. This process is usually referred to as the phase of coagulation andsyneresis. Hydrolysis of -casein during the primary phase of rennet action releases the highlycharged, hydrophilic C-terminal segment of -casein (macropeptide), as a result of which the zetapotential of the casein micelles is reduced from -10/-20 to -5/-7 mV and the protruding peptidesare removed from their surfaces, thus destroying the principal micelle-stabilizing factors

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(electrostatic and steric) and their colloidal stability. When roughly 85% of the total -casein hasbeen hydrolyzed, the stability of the micelles is reduced to such an extent that when they collide,they remain in contact and eventually build into a three-dimensional network, referred to as acoagulum or gel.16.3 Factors Affecting Rennet CoagulationThe primary and secondary phase of rennet coagulation are affected by some of the compositionaland environmental factors like milk composition, temperature, pH, calcium content, pre -heatingof milk, rennet concentration etc. The effects of all these factors are summarized here.16.3.1 Composition of milkVariation in the composition of milk mainly affects the rate of coagulation and the curd firmness.Fast coagulation results in firmer curd. The rate of clotting is largely dependent on the nature ofthe casein micelles and the equilibrium with the calcium phosphate and calcium ions. Thefirmness of the curd are affected by pH value, calcium concentration, temperature, fat content andthe ratio of rennin to casein. The rennet coagulation time (RCT) is markedly affected by theprotein content in milk. RCT decreases with protein content in the range of 2 -3%. Further increasein milk protein level i.e. more than 3% result in a slight increase in gelation time. This is due todecrease in rennet:casein ratio, which necessitates an increase in the time required to generatesufficient hydrolysis of -casein to induce aggregation of paracasein micelles. A minimum proteincontent of 2.5-3.0 is necessary to obtain gel in about 30 -40 minutes during cheese making. Increasein fat content also results in decreased RCT but the effect is lower than that of the protein content.16.3.2 Heat treatment of milkHeating milk to pasteurization temperature has beneficial effect on rennet coagulation due to heatinduced precipitation of calcium phosphate and a concomitant decrease in pH. But heating furtherto higher temperatures causes other effects which in combination dominate the positive effects ofheating to pasteurization. Some such effects are: whey protein denaturation and the interaction of denatured -lactoglobulin with micellar casein The deposition of heat-induced insoluble calcium phosphate leading to reduction in theconcentration of native micellar calcium phosphate. This micellar calcium phosphate is importantfor cross linking para--casein micelles and their aggregation during gel formation.16.3.3 Set temperatureThe principal effect of set temperature is on the secondary phase of enzymatic coagulation, whichdoes not occur at temperatures below around 18C. Above this temperature, the coagulation timedecreases to a broad minimum at 40-45C and then increases again, as the enzyme becomesdenatured. In cheese making, rennet coagulation normally occurs at around 31C. This isnecessary to optimize the growth of starter bacteria which will not survive the temperature morethan 40C. In addition, the structure of the coagulum is improved at the lower temperature, whichis therefore used even for cheeses made using thermophilic cultures.

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16.3.4 Rennet concentration

The rate of enzymatic coagulation is directly related to the concentration of enzyme. Increase inconcentration of rennet decrease RCT. During cheese making, rennet is added in such aconcentration so as to coagulate the milk 30-40 minutes. More rennet concentrations can be used toshorten the coagulation time but it leads to retention of more rennet in the curd which haspronounced effect in ripening of the cheese, particularly proteolysis. Some studies also suggestthat using increased concentration of rennet may jeopardize the curd firming rate and curdfirmness.16.3.5 Concentration of calcium ionsThe concentration of calcium ions mainly affect the secondary phase of enzymatic coagulation.Increased calcium concentration is beneficial for coagulation of milk. For this reason, sometimesCaCl2 is added to milk prior to cheese making. This promotes cheese making via three beneficialchanges, viz. an increase in calcium ion concentration, an increase in the concentrati on of colloidalcalcium phosphate and a concomitant decrease in pH (the addition of CaCl 2 to 0.02%, i.e. 1.8 mMCa, reduces the pH by ~ 0.05-0.1 units, depending on protein level).

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Module 8. Manufacture of different varieties of cheese

Lesson 17CHEDDAR CHEESE17.1 HistoryCheddar cheese originated from the village of Cheddar in Somerset, South West England.Cheddar Gorge on the edge of the village contains a number of caves, which provided the idealhumidity and constant temperature for maturing the cheese.Central to the modernization and standardization of Cheddar cheese was the nineteenth centurySomerset dairyman Joseph Harding. Owing to the technical developments, promotion of d airyhygiene and unremunerated propagation of modern cheese-making techniques he suggested, hehas been described as the father of Cheddar cheese. Harding introduced new equipment into theprocess of cheese making, including his revolving breaker for curd cutting, saving much manualeffort. The Joseph Harding method was the first modern system for Cheddar production basedon scientific principles. He and his wife were behind the introduction of the cheese into Scotlandand North America. Joseph Harding's son, Henry Harding, was responsible for introducingCheddar cheese production to Australia.Cheddar is the most popular cheese in the United Kingdom, accounting for 51% of the country's1.9 billion annual cheese market. In 2010, the UK produced 2,58,000 tons of Cheddar cheese. It isthe second most popular cheese in the USA (behind Mozzarella), with an average annualconsumption of 4.5 kg per capita.17.2 Chemical CompositionTable 17.1 Composition of Cheddar cheese made from cow and buffalo milk

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17.3 Method of Manufacture

The manufacturing of Cheddar cheese consist of (a) addition of starter culture to milk; (b)coagulating milk; (c) cutting the resultant coagulum into small cubes; (d) heating and stirring thecubes with the concomitant production of a required amount of acid; (e) whey removal; (f) fusingthe cubes of curd into slabs by cheddaring; (g) milling the cheddared curd;(h) salting ; (i)pressing ; (j) packaging and ripening. The detailed method is shown in Fig. 17.1.17.3.1 CheddaringSteps upto cutting, cooking and whey removal are similar to the other varieties of cheese but thestep which separates Cheddar cheese from other varieties is cheddaring. It is a step whichinvolves a series of operations consisting of packing, turning, piling and re-piling the slabs ofmatted curd. This process of piling and re-piling is repeated every 15 min. This process squashesthe individual curd particles as well as releases more whey. In this process, the curd granules fuseunder gravity into solid blocks. Rapid matting of the curd particles occurs under the combinedeffect of heat and acid. The original rubber-like texture gradually changes into a close-knit texture(chicken breast structure, typical of Cheddar cheese) with the matted curd particles becomingfibrous. When the acidity of whey reaches 0.45-0.50% and cheddaring is complete, the curd ismilled. The milled curd is salted, pressed, packaged and kept for ripening in the manner followedfor all cheese varieties.Later research has suggested that cheddaring is not an essential step and serves no purpose otherthan to provide a holding period which is required for acidity development and whey removal.The major factors affecting the process of whey removal are acidity and temperature of the curd.Mechanical forces (pressure and flow) are important in the development of fibrous structure in thecurd. Fibrous structure cannot be brought about by pressure and deformation unless the curd hasreached a pH of 5.8 or less. This suggests that pressure and flow serve to knit, join, stretch andorient the network of casein fibres already formed in response to rising acidity. This structureformation is also influenced by temperature and moisture.17.4 Texture of Cheddar CheeseCheddar cheese has a texture that is intermediate between those of high pH cheese (Goudacheese), which flows readily when a force is applied and the low pH cheeses (Cheshire) whichtend to deform, by shattering, only at their yield point. Much of the protein in Cheddar cheese isin the form of smaller particles than Gouda. As the pH decreases towards that of the isoelectricpoint of paracasein, the protein assumes an increasingly more compact conformation and thecheese becomes shorter in texture and fractures at a small deformation.17.5 Flavor of Cheddar CheeseFlavor of Cheddar cheese is affected by a number of factors like milk fat, proteolysis, starter andnon-starter bacteria etc. It has been studied that when a series of batches of Cheddar cheese weremade with fat content increasing from 0 to 4.5%, the flavor improved as the fat content increasedbut above a certain limit, there was no increase in flavor. This suggested that the water -fatinterface is important and the flavor components are dissolved and retained in the fat. Thu s, it isclear that fat plays an important role in flavor development of Cheddar cheese. As breakdown ofcasein is also involved in the production of Cheddar cheese flavor, proteolysis plays a major rolein flavor development. Other than milk fat and proteolysis, the factors that affect flavor ofCheddar cheese are starter and non-starter bacteria.

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Fig. 17.1 Flow diagram for Cheddar cheese

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LESSON 18GOUDA CHEESE18.1 IntroductionGouda cheese, originated in the vicinity of Gouda in the province of South Holland, is one of themost important Dutch type varieties of cheese produced in the world. It belongs to semi -hard tohard varieties of cheese with few or no eye holes. Dutch type varieties of cheese are those that aremade from fresh cows milk having fat such that the product contains at least 40% fat in the drymatter, starters consisting of mesophilic lactococci and leuconostocs that produce CO 2 , clotted byrennet, pressed to obtain a close rind, are salted in brine after pressing and have no essentialsurface flora (Walstra et al., 1998).

Fig 18.1 Gouda cheese with small eyes

Traditionally, two main types of cheese were made in the Netherlands, namely Gouda and Edam.Gouda cheese was made from fresh unskimmed milk and was matured for 6-60 weeks whileEdam cheese was made from a mixture of skimmed evening milk and fresh morning milk suchthat fat in cheese is about 40% on dry matter basis. The cheese has a somewhat shorter texturethan Gouda and was usually ripened for 6 months or more.Table 18.1 Chemical Composition

18.2 Method of Manufacture

18.2.1 Standardization, renneting and cuttingFor the manufacture of good quality Gouda cheese, cow milk is considered to be the most suitableraw material. Manufacturing of Gouda cheese starts with acidification of the standardized milk.67

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The milk is standardized so as to give 40-50% fat in cheese on dry matter. Starter is added @ 0.7%of the milk. No ripening is done for this type of cheese. Renneting is usually done at about 30C @0.022% of milk and allowed to set for about 20-30 minutes. After the curd is properly set, it is cutin cubes of some 8-15 mm size. Stirring, at first gently till acidity rises by 0.02% (to minimize lossof fines) and later more vigorously, is done with the knives used for cutting or with specialstirrers.18.2.2 ScaldingAfter cutting, part of the whey (about one third) is removed for more effective stirring and topromote syneresis. It also facilitates partial removal of lactose, which aids in achieving a loweracidity. The temperature is also increased at the same time to aid syneresis process but not toohigh to injure starter organisms. Usually, it is kept below 38C. This process of heating curd inwhey is called scalding. The temperature is increased usually by addition of hot water at about60C (about equal quantity of whey drained) which also helps in controlling water content and thepH of the cheese.18.2.3 Draining and pressingAfter the curd has lost enough moisture i.e. around 65% moisture is left in the curd and pH isaround 6.5, stirring is stopped and the curd grains are allowed to sediment. Continuous mass ofcurd is then formed due to fusion of the curd grains. This curd can now be cut into blocks andtaken out of the whey. Blocks may be pressed further to remove whey. This may also causeconsiderable loss of fines. Fat loss in whey can be recovered by passing it through cream separatorand loss of fines can be recovered by the use of hydrocyclones. The blocks are then put intomoulds and pressed.18.2.4 BriningBrine salting is generally done using about 18-20% brine in tank. The pH of brine is adjusted to4.8-4.9 to prevent dissolution of cheese protein in the brine. Cheese blocks should be inverted fewtimes daily. Time taken for brining will depend on size, viz., 0.45 kg - 20 h, 0.90 kg - 36 h, and 3.83kg - 3 days.After brining, paraffining is done and the cheese blocks are kept for ripening. A maximum of 3-4months are required for development of flavour and texture of Gouda cheese.

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Fig. 18.2 Flow diagram for manufacturing Gouda cheese

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Lesson 19SWISS CHEESE19.1 IntroductionSwiss cheese originated in the Emme valley in Switzerland around the 15th century. It is known asEmmental cheese in the country of its origin. Besides the USA and Switzerland, many othercountries such as Italy, Austria, Finland, Denmark, Germany and Argentina are known to makeexcellent Swiss cheese.This cheese is a hard variety, known by the presence of shining eyes with smooth, waxy textureand sweet nutty taste with a mild flavor. It is reported that a specific grass available in the Emmevalley produce typical cheese, this being the probable reason that no other country has duplicatedexactly, the flavor and body characteristics of Emmental cheese from Switzerland. Swiss cheeseshould have a sliceable texture, regular round eye holes, dull to brilliant appearance, 45% min faton dry matter basis, mild nut-like taste and should be minimum of 60 days old beforeconsumption. Swiss cheese production ranks third in the world, next only to Cheddar andMozzarella.Table 19.1 Composition

19.2 Mechanism of Eye Formation

Most Swiss-type cheeses undergo a more or less pronounced propionic acid fermentation, whichis brought about by propionic acid bacteria. They grow under anaerobic conditions, using calciumlactate as the substrate. The end products are the corresponding propionate, acetate, water andcarbon dioxide.Part of the CO 2 may be produced by dicarboxylation of amino acids (e.g. tyrosine and arginine) byenterococci due to high salt concentration and low pH (5.1 to 5.2) in the periphery of the cheese. Ithas been reported that 50% of the lactate is metabolized by propionibacteria and lactatefermentation is more intense in the centre than in the periphery.To initiate propionic acid fermentation, the ripening temperature of the cheese must be raisedapproximately to 18-25oC for a certain period of time. The relative humidity (RH) of the curingroom during hot curing (22 oC/85% RH/6-8 weeks) influences the eye formation. Uneven RHresults in uneven eye formation. The eyes are formed by the continuous production of CO 2 whichdiffuses out at weak points. They have 1.252.54 cm diameter and are spaced at 2.54 7.62 cm. As

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soon as the development of sufficient eyes is accomplished, the propionic acid fermentation isusually retarded by storing the cheese at lower temperatures. About 130 l of CO 2 is produced in120-150 days in 80 kg Swiss cheese where 80 l of CO 2 diffuses out and 50 l of it remains in the eyesat 85 92% RH.19.3 Method of manufacturing

Fig 19.1 Steps of Manufacture

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19.4 Defects19.4.1 Late fermentationThis occurs during ripening of cheese. The gas may form pin holes or the resulting eyes mayappear in clusters. This defect is usually caused by lactate fermenting bacteria belonging to thegenus Clostridium, strains of butyric acid bacteria, the name usually used by Swiss cheese makersfor those organisms isolated from brown cheese. Among the various species like Clostridiumtyrobutyricium, C. butyricum and C. sporogenes, it has been found that only C.tyrobutyricum produces brown cheese.19.4.2 Bitter CheeseStreptococcus faecalis var. liquefaciens forms the major part of the ripening flora and is directlyresponsible for bitterness. Generally, this is not caused by a detrimental flora, but by some starterstrains that may not contain enough peptidases to degrade the peptides produced by proteolysis.This may result from the higher proteolytic activity of the rennet at lower pH, which leads toaccumulation of polypeptides including bitter ones. Cheese manufactured using temperatureshigher than normal has a greater incidence of bitterness than those made by traditional methods.19.4.3 Flavor DefectsThe most common among these are putrid, unclean, fermented, yeasty, rancid and fruity. Putridflavor is probably caused by objectionable protein decomposition and the odor frequentlyresembles H2 S with equally offensive aromas. Large numbers of Clostridia and Micrococci havebeen found in such spoiled cheeses. Clostridium lentoputrescens is associated with a putrid flavorand with development of a white, crumbly conditions and large irregular eyes.Rancid flavor is usually because of higher concentrations of butyric acid produced by C.butyricum or C. tyrobutyricum. Oxidative rancidity resulting from lipid oxidation also may occur.Use of lipolysed milk may also yield rancid cheese.19.4.4 Colour DefectsColored spots may be formed by the growth of pigmented propionibacteria in Swiss cheese. Theround brown spots on the cut surface or eyes of cheese could be overcome by adding starterpropionibacteria. This defect is most pronounced when cows are not on pasture and when milkcontains fewer propionibacteria. Propionibacterium rubrum and P. theonii are brightly colored andmay cause spots. Dark spots may be caused by other pigmented microorganisms.

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Cheese TechnologyTable 19.2 Defects in Swiss cheese

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Lesson 20MOZZARELLA CHEESE20.1 IntroductionMozzarella cheese was originally manufactured from high fat buffalo milk in the Battipagliaregion of Italy, but it is now made all over Italy, in other European countries and USA from cowmilk. It belongs to the cheese classified as pasta filata which involves the principle of skillfullystretching the curd in hot water to get a smooth texture and grain in cheese. It is a soft, white unripened cheese which may be consumed shortly after manufacture. Its melting and stretchingcharacteristics are highly appreciated in the manufacture of Pizza where it is a key ingredient.The method of manufacture of Mozzarella cheese, irrespective of the milk system from which it ismade involves (1) optimum addition of starter culture or proper acidification of milk, (2)renneting of milk, (3) cutting the curd at the right firmness, (4) stirring and cooking the curdparticles to the correct consistency and (5) proper cheddaring, stretching and salting of curd fo roptimum plasticity and elasticity.Table 20.1 Chemical composition

20.2 Chemistry of stretch of Mozzarella Cheese

In the calcium rich environment of milk, the casein precipitates out of milk as di -calciumparacaseinate, entrapping fat, insoluble minerals and some sugar. At a pH between 5.2-5.4,resulting from the development (or direct introduction) of acid, some of the calcium of thedicalcium paracaseinate gets dissolved, leading to the formation of monocalcium paracaseinate.This when heated to 54C or higher becomes smooth, pliable and stringy and retains fat. Ifacidification is excessive, generally below pH 5.2, monocalcium paracaseinate will continue to losecalcium and form paracasein, which may stretch, but has difficulty in retaining fat. T he curdgenerally does not stretch above pH 5.6.

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Fig 20.1 Manufacturing steps (Traditional method)

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Fig 20.2 Manufacturing Steps (Direct Acid Method)

20.3 Advantages of the Direct Acidification Technique1) Curtailed manufacturing time and expenses2) Simplified technology due to elimination of propagation and maintenance of starter cultures3) Starter failures due to bacteriophages and antimicrobial agents avoided4) Less rennet required5) Amenable to mechanization76

Lesson 21COTTAGE CHEESE21.1 Definitiona) Cottage cheese is a soft, unripened cheese that is usually made from skim milk. It has a mildacid flavor. It consists of small particles or flakes of curd, which have a meaty consistency.b) Creamed Cottage cheese is cheese which is mixed with cream so that the mixture contains notless than 4% fat. Both Cottage cheese and creamed Cottage cheese are usually salted.21.2 Method of Manufacturea) There are two methods of manufacture i) Milk coagulated by acidity developed by the action oflactic starter, ii) Coagulation accomplished by the combined actions of lactic starter and a smallquantity of rennet.b) The two types of curd may be characterized as below:Table 21.1 Types of curd

21.2.3 RennetRennet, if added, is at the rate of 15 mg per 100 l milk. Rennet diluted about 40 times with potablewater for uniform distribution. Calcium chloride may be added (before adding rennet), if desired,for firm curd formation. Color may be added @ 0.5-1.0 ml/100 l (before adding rennet), if desired.The most desirable titratable acidity of whey at cutting is approximately 0.5% (optimum pH 4.6 4.7). The whey must come from interior of curd and must be clear and free from curd particles. Ifthe acidity is too low at cutting, curd develops a rubbery consistency. Too high acidity results inshattering of curd, giving low yield. Method of cutting and size of curd cubes is same as forCheddar cheese.21.2.4 CookingCooking begins soon after cutting and continues for 12 h until temperature is about 46 oC or untilcurd becomes firm enough to remove whey. Stirring during heating kept at a minimum and isvery gently done in the early stages. The temperature is increased slowly at first. The finaltemperature is attained in 11/2 to 2 h.21.2.5 Removal of wheyWhey is removed when curd cubes have no soft centres and when a handful of them squeezedgently show slight elasticity. The whey is removed from curd approximately 2 h after cutting. Atthis time the size of curd cubes approximate two third of their original volume. The drainage ofwhey is done the same way as for Cheddar cheese.21.2.6 Washing the curdThe curd is washed after all the whey has been removed. This treatment makes the curd firme rand hard to touch; it also removes acid whey from around it and aids in producing desiredmildness in flavor. The wash-water is applied in at least two treatments. The first is at atemperature of about 21oC and in amounts not less than twice the volume of curd in the vat. After15 minutes soaking of cubes, the wash-water is removed. The second (or third, if necessary) washwater is at 15oC or lower, in amounts as above.21.2.7 DrainingDraining should be thorough. It is best done by placing curd cubes in a draining rack withperforated bottoms, which can be wheeled into rooms under refrigeration.21.2.8 SaltingSalting is done when free moisture is drained from the curd. Salt can be applied to the curd in thevat or it can be dissolved in the cream for creamed Cottage cheese. It is usually done in 2applications. Coarse salt preferred. Salt is added @ 1% or curd weight of 1.5 kg/1000 kg milk.Salted or unsalted curd is held at about 2 oC till shipping.21.2.9 CreamingCottage cheese is creamed immediately after draining, if the product is to be packaged at once.Holding the curd overnight in a cold room before creaming makes it more firm at creaming.

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Calculated amount of 20% cream is homogenized before mixing so as to form a thick glossycoating over the curd particles.

Figure 21.1 Manufacture of cottage cheese

21.2.10 YieldThe yield of curd before creaming depends essentially upon:i) The composition of milkii) The manufacturing lossesiii) The moisture content of the cheeseWhile the approximate yield of uncreamed Cottage cheese is 15% of milk, that of creamed Cottagecheese (with 20% fat in cream and 4% fat in finished product) is 18.3%. The yield of Cottage cheeseis given by the formula:

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21.2.11 Keeping quality

Both Cottage cheese and creamed Cottage cheese have short keeping quality even underrefrigerated storage (5-10oC). Uncreamed Cottage cheese may be preserved for 90 days or longerby freezing or by brine storage. However, quality will deteriorate because freezing often leads tograininess and curd shattering, particularly with rennet cheese.

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Module 9. Changes during ripening of cheese

Unique characteristics of each cheese variety are determined by the curd manufacturingoperations but these characteristics are largely developed during ripening process. For example,the type of microflora established in the curd is determined by the manufacturing process but itseffect on cheese characteristics develop largely during the ripening proce ss.Ripening involves microbial and chemical changes which are responsible for development oftypical characteristics of varieties of cheeses. Microbial changes involve death and lysis of thestarter cells, development of non-starter microflora and growth of secondary microflora. Ripeningusually causes softening of the cheese texture due to hydrolysis of the casein matrix, change in pHand change in water binding ability of the curd. Flavor production is largely described by a seriesof biochemical events taking place during ripening.The primary events occuring during cheese ripening are metabolism of residual lactose, lactatemetabolism, proteolysis and lipolysis. These reactions are mainly responsible for textural changesand development of flavor in cheese. However, many secondary changes occur simultaneouslyand modify cheese texture and flavor. Since the biochemistry of cheese ripening is complex, theobjective of this chapter is to present an overview of the principal biochemical pathwayscontributing towards cheese ripening.22.2 Metabolism of Residual LactoseLactic acid bacteria (LAB) is added in the form of starter culture to cheese metabolize lactose tolactate. The rate and extent of acidification influence texture of the curd by controlling the rate ofdemineralization. The pH of the cheese curd is largely determined by the extent of acidificationduring manufacturing process. This influences the solubility of the casein, which in turn affectsthe texture of curd. pH also affects the activity of enzymes involved in ripening, thereby having anindirect effect on cheese texture and flavor development.Most of the lactose is lost in whey during cheese manufacturing. However, low levels of lactoseremains in the curd. This residual lactose is converted to L-lactate during early stages of ripeningby the action of starter bacteria. The rate of conversion is dependent on temperature and salt-inmoisture levels of the curd. Starter activity is stopped very quickly at the end of manufacturingoperations due to low pH, salt addition and lesser amount of fermentable lactose. Lactose thatremains unfermented by the starter is probably metabolized by non-starter lactic acid bacteria(NSLAB) flora present in curd and they convert the residual lactose to D-lactate. D-lactate can alsobe formed by the racemisation of L-lactate.22.3 Lactate MetabolismLactate produced by fermentation of residual lactose serves as an important substrate for a rangeof reactions occuring during cheese ripening. L-lactate can be racemised to D-lactate by NSLAB82

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flora. D-lactate is less soluble than L-lactate which results in the formation of Ca-D-lactate crystals.These crystals are not harmful but they appear as white specks on the surface of the maturecheese.Lactose can be metabolized to acetate, ethanol, formate and CO 2 depending on the population ofNSLAB and availability of O2 . In cheese wrapped with film, oxidation of lactate occurs to a lesserextent due to low level of O2 available.Late gas blowing is a defect which is caused by anaerobic metabolism of lactate by Clostridiumtyrobutyricum to butyrate and H2 . The release of H2 causes cracks in cheese during ripening.The above mentioned metabolisms contribute negatively towards cheese ripening. There are somepositive contributions also of lactate metabolism. This is essential for cheese varietiescharacterized by the development of large eyes during ripening such as Emmentalcheese. Propionibacterium freudenrichii metabolise lactate to propionate, acetate, CO2 and H2 O.Propionate and acetate contribute to the flavor of cheese while CO 2 is mainly responsible for eyeformation.22.4 LipolysisMilk fat is essential for the development of the correct flavor in cheese during ripening. Cheddarand other cheeses normally made from whole milk do not develop correct flavor when made fromskim milk or milks in which milk fat has been replaced with other lipids. Lipids may undergooxidative or hydrolytic degradation in foods but the redox potential of cheese is very low, somainly hydrolytic degradation of lipids takes place in cheese. The triglycerides present in cheeseare hydrolyzed by lipases which result in the formation of fatty acids.Sources of lipases in cheese are: Milk (particularly unpasteurized) Rennet Starter culture Starter adjuncts Non starter bacteria (may come through ingredients or contamination) Exogenous lipase (if added deliberately)Low level of lipolysis is required for the development of flavor of cheese but excessive lipolysiscauses rancidity. Lipolysis of milk fat results in production of free fatty acids which contribute tothe flavor of cheese and also act as precursors for development of other flavor compounds incheese like esters, lactones, ketones and aldehydes. These secondary fat-derived compounds canbe very potent flavor compounds.Fatty acid esters are produced by reaction of fatty acids with an alcohol; ethyl esters are mostcommon in cheese. Thioesters are formed by reaction of a fatty acid with a thiol compoundformed via the catabolism of sulphur-containing amino acids. Fatty acid lactones are formed bythe intramolecular esterification of hydroxyacids; - and -lactones contribute to the flavor of a83

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number of cheese varieties. n-methyl ketones are formed by the partial -oxidation of fatty acids.Liberation of short and medium chain fatty acids from milk fat by lipolysis contribute directly tocheese flavor. This degree of flavor development depends on the variety of cheese. For example, itis very extensive in some hard Italian varieties, smear cheeses and blue mold cheeses. Excessivelipolysis causes rancidity in cheese varieties like Cheddar and Gouda.

Fig. 22.1 Production of flavor compounds from fatty acids during cheese ripening22.5 ProteolysisProteolysis is the most important and complex of all the events during ripening of cheese. Theextent and pattern of proteolysis is also used as an index of cheese ripening and quality of cheese.Proteolysis contributes significantly towards development of texture and fl avor in cheese. Texturalchanges (softening of cheese curd) occur due to breakdown of protein network and release ofcarboxyl and amino groups resulting in the binding of more water and thus decrease wateractivity (aw). Proteolysis leads to the formation of peptides and free amino acids which contributeto cheese flavor. These amino acids also act as precursors for many reactions like transamination,deamination, decarboxylation, desulphuration, catabolism of aromatic compounds such astyrosine, phenylalanine, tryptophan, etc. and generate many important flavor compounds.Proteolysis in cheese is catalysed by proteinases and peptidases and they originate from thefollowing sources: Coagulant Milk Starter LAB Non starter LAB Secondary starters (e.g. P. camemberti in Camembert cheese and P. roqueforti in Blue cheese) Exogenous proteinases or peptidases, if added for accelerated ripening of cheese84

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In majority of cheese varieties, casein is initially hydrolyzed by the residual coagulant, oftenchymosin, which results in formation of large and intermediate-sized peptides. These peptides arethen hydrolyzed by enzymes derived from starter and non-starter microflora of the cheese. Theproduction of small peptides and amino acids is caused by the action of microbial proteinases andpeptidases, respectively.The final products of proteolysis are amino acids, the concentration of which depends on thecheese variety. The concentration of amino acids in cheese at a given stage of ripening is the netresult of the liberation of amino acids from the caseins by proteolysis and their catabolism ortransformation into other amino acids by the cheese microflora. Medium and small peptidescontribute to a brothy background flavor in many cheese varieties; short, hydrophobic peptidesare bitter. Amino acids contribute directly to cheese flavor as some amino acids taste sweet (e.g.Gly, Ser, Thr, Ala, Pro), sour (e.g. His, Glu, Asp) or bitter (e.g. Arg, Met, Val, Leu, Phe, Tyr, Ile,Trp).

Fig 22.2 Proteolysis in cheese during ripening

22.6 Microbiology of Cheese RipeningMicroorganisms including bacteria, yeasts and molds are present in cheese and contribute to theripening process through their metabolic activity. The enzymes released by these microorganismsalso add to the various metabolic activities like proteolysis, glycolysis and lipolysis.Microorganisms in cheese may gain entry through their intended addition in the form of starterculture and they may be associated with the ingredients used in cheese making. The microfloraassociated with cheese ripening may be divided into two groups - the starter bacteria and non-

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starter bacteria. Starter bacteria are primarily responsible for acid production during manufactureto reduce the pH of milk to the desired level. The secondary microflora do not play any active roleduring cheese manufacture but contribute to the ripening process.The factors controlling the growth of microorganisms in cheese include water activity,concentration of salt, oxidation-reduction potential, pH, ripening temperature, and the presence orabsence of bacteriocins (produced by some starters).22.6.1 Water activityWater activity (aw) is defined as the ratio of the vapor pressure of water in a material (p) to thevapor pressure of pure water (po) at the same temperature. Its value ranges from 0 to 1.0. Itexpresses the water availability rather than total water present in the system. Water activity ofcheese reduces during ripening process. This may be due to several reasons like: Evaporation of moisture if the cheese is not vacuum packed or paraffin coated Hydration of proteins bound water rendering it unavailable for bacterial growth Hydrolysis of proteins to peptides and amino acids and of lipids to glycerol and fatty acids The salt and organic acids (lactate, acetate, and propionate) dissolved in the moisture of thecheese reduce the vapor pressureGrowth of microorganisms at low aw is characterized by a long lag phase, a slow rate of growth,and a reduction in the maximum number of cells produced. Each of these factors helps to limit thenumber of cells produced. LAB generally have higher minimum aw values than other bacteria.The amount of salt in moisture in cheese also affects the growth of microorganisms in cheese.The salt normally used in cheese making is about 2% of the weight of the curd. Salt is added tocheese mainly to suppress growth of unwanted microorganism and to assist the physico -chemicalchanges in the curd. The growth of unwanted microorganisms is essenti ally curbed by reductionin aw as salt act as a humectant.22.6.2 Oxidation-Reduction potentialThe oxidation-reduction potential (Eh) is a measure of the tendency of the solution to either gainor lose electrons when it is subject to change by introduction of a new species. The Eh of milk isabout +150 mV whereas that of cheese is about -250 mV. As cheese ages, the products ofproteolysis and lipolysis may reduce the Eh of cheese. This reduction of Eh makes cheese ananaerobic system, in which only facultatively or obligately anaerobic microorganisms can grow.Anaerobic sporeforming organisms present in the cheese may germinate and grow, causingdefects like bitter and putrid flavor. Obligate aerobes, like Pseudomonas spp., Brevibacterium spp.,and Micrococcus spp., will not grow within the cheese, even when other conditions for growth arefavorable. Eh is therefore important in determining the types of microorganisms that grow incheese.22.6.3 pHMost bacteria require a neutral pH value for optimum growth and grow poorly at pH valuesbelow 5.0. The pH of cheese curd after manufacture generally lies within the range 4.5-5.3, so pHis also a significant factor in controlling bacterial growth in cheese. LAB, especially lactobacilli,86

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generally has pH optima below 7, and Lactobacillus spp. can grow at pH 4.0. Most yeasts andmolds can grow at pH values below 3.0, although their optimal range is from 5 to 7. B. linens, animportant organism in smear-ripened cheese, cannot grow below pH 6.0. Micrococcus spp., whichare commonly found on the surface of soft cheeses, cannot grow at pH 5 and only slowly at pH5.5.22.6.4 TemperatureThe ripening temperature of cheese mainly depends on two considerations: the temperatureshould be such that the growth of undesirable spoilage causing and pathogenic bacteria can bechecked and at the same time, this temperature should be conducive for various ripeningreactions essential for development of typical flavor, body and texture of cheese. Ripeningtemperature for Cheddar cheese is 6-8C while Camembert and other mold-ripened cheeses areripened at 10-15C. Emmental cheese is ripened initially for 2-3 weeks at a low temperature (~12C), after which the temperature is increased to 20-24C for 2-4 weeks to promote the growth ofpropionic acid bacteria and the fermentation of lactate to propionate, acetate, and CO 2 . Thetemperature is then reduced again to around 4C. Use of higher ripening temperature is one of thetechniques used for accelerated ripening of cheese but it also stimulates the growth of othermicroorganisms present in cheese.

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Module 10. Yield of cheese

Lesson 23CHEESE YIELD, MEASUREMENT OF CHEESE YIELD23.1 IntroductionThe yield of cheese and its control are of great economic importance, determining the profit ofcheese plants and the price of milk given to farmers. Therefore, cheese yield and the factors thataffect it need to be studied thoroughly. Cheese yield calculation is important for measuring theefficiency of and determining the economic viability of a cheese making operation. It also aids inevaluating the potential usefulness of a particular process or change in technology.23.2 DefinitionCheese yield may be expressed as the quantity of cheese of a given dry matter produced from agiven quantity of milk with a defined protein and fat content (kg/100 kg milk). Actual cheeseyield (Ya) is often slackly expressed as the kilogram of cheese per 100 kilograms of milk or percent yield.23.3 Measurement of Cheese YieldMeasurement of cheese yield requires determination of weight of all the inputs and outputs. Thiscan be easily achieved in a pilot scale plant where cheese is made in batches but incommercial/large scale cheese manufacturing, this cannot be done batchwise. In such plants, yieldis calculated on daily basis rather than calculating it batchwise. Once all the inputs and outp utsare determined, the actual yield can be calculated as:

Although all different varieties of cheeses have standard limit for maximum moisture content,some batch to batch variations are unavoidable. Thus comparing yields of cheese having differentmoisture content is erroneous. To avoid the effect of moisture content, yield can be calculated byusing the following equation:

Other than moisture, many factors affect the yield of a particular variety of cheese, including themilk composition, the cheese making process, and the type of plant equipment. The latter twofactors influence cheese yield, since they affect the recovery of milk fat and protein in the cheese. Ifa manufacturer wants to compare cheese yields of different days in a year, then comparing the88

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actual yield (Ya) or MCY would be erroneous as the yield is also affected by the actual recovery offat and protein in cheese and also by the composition of the raw milk. In this situation, if thecomposition of the cheese milk (protein and fat) and the cheese (protein, fat, and salt) at thedifferent manufacturing times are known, the yield of cheese at the different times may bemeaningfully compared by adjusting the protein and fat content of the milk to reference values.The resulting yield expression is termed the moisture-adjusted cheese yield/100 kg milk adjustedfor protein and fat (MACYPF):

The above equation assumes that casein content of protein is not changing over time. If it is proneto change over time, then protein content may be replaced by casein content in the same equation.23.4 Prediction of Cheese YieldCheese yield is mainly affected by fat and casein content of milk and recovery of thesecomponents in the final product. A general formula for calculating yield may be expressed as Y=aF + bC, where Y is the yield, F and C are fat and casein contents in milk respectively, and a and bare the coefficients which are related to fat loss and casein recovery during manufacturing process.Several formulae are developed for prediction of cheese yield, depending on the cheese varietyand composition of the cheese milk. Predictive yield formulae are useful in a cheese plant tomeasure its efficiency by comparing actual and predicted yields, for better production planningand also to plan product mix. Formulae for some varieties of cheese are given below:23.4.1 Cheddar cheeseVan Slyke and Price Formula:

Where TS= total solids of skim milk

These formulae are established on the basis of average fat loss in whey and during other processeslike plasticizing in Mozzarella cheese, average loss of casein in whey and increase in the weight ofcheese due to other constituents and the added salt. For instance, in the formula for Cheddarcheese, 0.93 is the percent recovery of fat, C0.10 indicates 10% loss of casein and factor 1.09 is forincrease in the weight of cheese by other constituents of milk and added salt.

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Lesson 24FACTORS AFFECTING CHEESE YIELD24.1 Factors Affecting Cheese YieldFactors affecting cheese yield can broadly be listed into two groups:24.1.1 Cheese yield potential of milki) Breed of cowii) Variation between individual cowsiii) Stage of lactationiv) Seasonal changes in climate and natural feedv) The type of feed and level of feedingvi) Problems due to diseases, especially mastitisvii) Milking procedures, such as the time that elapses between milkings and whether milked byhand or by machinesviii) Effect of genetic variants on milk composition24.1.2 Processing conditions that affect cheese yieldi) Storage of milkii) Milk standardizationiii) Concentration of milkiv) Growth media used for bulk starter preparationv) Type of starter culture usedvi) Heat treatment of milkvii) Homogenization of milkviii) Addition of CaCl 2 to milkix) Type of coagulant used

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x) Curd firmnessxi) Type of vatxii) Curd handling systemxiii) Cooking of curdxiv) Cheddaring of curdxv) Washing of curdxvi) Proportion of salt addedxvii) Pressure appliedxviii) Loss of moisture during storageThe major factors that affect yield of cheese are discussed here. They can be broadly classified intwo categories: 1) Uncontrollable factors and 2) Controllable factors. The major factor which isbeyond the control of a cheese maker is the composition of milk. The other uncontrollable factor isthe equipment used by the cheese maker. Various controllable factors are those related to themethod of manufacturing and the processing conditions used while cheese making. The principalfactors that influence cheese yield are discussed below:24.1.3 Milk compositionOne of the most important factors that affect cheese yield is the milk composition particularlycasein and fat content. As already mentioned, cheese yield can be predicted by using the generalequation Y= aF + bC. This shows that cheese yield is linearly related with fat and casein content ofmilk. The greater contribution of casein is expected, as it forms the continuous paracasein sponge like network that occludes the fat and serum phases. In contrast, fat on its own has little waterholding capacity. Occluded moisture contributes directly to cheese yield and i ndirectly owing tothe presence of dissolved solids, including whey proteins, -casein glycomacropeptide, lactate,and soluble milk salts. Fat generally contributes more than its own weight to Cheddar-type cheese(yield increases by about 1.16 kg/kg milk fat). This greater than pro-rata increase, is due to theincrease in the level of moisture in nonfat substance as the fat content of the cheese increases. Fatis occluded in the pores of the paracasein network of the cheese and impedes syneresis. Theoccluded fat globules physically limit aggregation of the surrounding paracasein network andtherefore reduce the degree of matrix contraction and moisture expulsion. Hence, as the fatcontent of the curd is increased, it becomes more difficult to expel moisture , and the moistureprotein ratio increases. However, if the moisture in nonfat substance is maintained constant (e.g.by process modifications such as reduction of curd particle size and slight elevation of the scaldtemperature), fat contributes less than its own weight to cheese yield (~ 0.9 kg/kg), owing to thefact that about 8-10% of the milk fat is normally lost in the whey.The coefficients a and b depend on the composition of milk, the manufacturing procedure,equipment design and retention of fat and casein in the cheese. All those factors that affect milkcomposition, indirectly affect the yield also. Some such factors are species and breed of the animal,stage of lactation, seasonal variations, etc.92

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24.1.4 Holding milk at low temperature

When it is not possible for the cheesemakers to start cheese making soon after milk reception, themilk is stored in cold storages for some hours, depending on the manufacturing schedule. Thisaction of storing milk at refrigerated temperature results in some physico-chemical changes inmilk, which include: Solubilization of casein and colloidal calcium phosphate which leads to increase in serumcaseins, thereby increasing loss in whey. Growth of psychrotrophic bacteria which leads to release of enzymes like proteases and lipases. Increase in free fat levels owing to lipase action.The increased serum casein level can be reversed by pasteurization and thus, the effect of coldstorage is nullified but the production of proteases cause protein breakdown into peptides. Someof these peptides are soluble in the serum phase and do not coagulate during curd formation.They are lost in whey leading to a decrease in cheese yield. The reduced casein level has an effectof curd shattering and weak coagulum, thereby increasing fat loss in whey. The dual effect oflosing casein and fat in whey reduces the cheese yield considerably.24.1.5 Heat treatment of milkCheese milk can be given heat treatments like thermization, pasteurization, etc. Heat treatmentdenatures whey proteins and results in their inclusion in the gel and thereby increase yield ofcheese. The degree of whey protein denaturation determines the extent of their recovery in cheese.Thermization is done when milk is to be stored for long before making cheese. As discussed in theprevious section, cold storage of milk leads to production of enzymes like proteases and lipases.Thermization prevents growth of psychrotrophs in milk, prevents casein solubilization and thusincreases cheese yield. Pasteurization of milk (72C, 15 s) denatures whey proteins to a lower leveland thus the cheese yield is only slightly increased. The severe the heat treatment, more is theresultant increase in cheese yield.24.1.6 Addition of CaCl2Addition of CaCl 2 at the rate of 0.02% in cheese milk is a common practice. This results instrengthening the curd, making it less susceptible to shattering at the time of cutting and stirring.This reduces the chances of fat and protein loss in whey and thus increases cheese yield.24.1.7 Type of rennetType of rennet used for coagulation affects cheese yield as it affects the extent of proteolysis. Therennet having more proteolytic activity solubilizes casein and increases its loss in whey.Proteolytic rennet reduces cheese yield significantly only when the pH of the whey at the time ofdrainage is below 6.0 as in the case of Blue cheese and Camembert cheese.

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Module 11. Cheese from buffalo milk

Lesson 25PROBLEMS IN BUFFALO MILK CHEESE MAKING25.1 IntroductionMost of the well known cheese varieties of the world are conventionally produced from cow milk.However, buffalo milk too has been utilized with considerable success for manufacture of certainvarieties of cheeses. Cheese made from buffalo milk displays typical body and texturalcharacteristics. More specifically, where chewing and stringing properties are especially desired asin case of Mozzarella cheese, buffalo milk is technologically preferable over cow milk. In Italy,fresh and Pasta Filata cheese, especially Mozzarella, has been traditionally prepared from buffalomilk. In Balkan countries, several types of white brined and pickled cheeses are prepared frombuffalo milk. Feta (Greece), Domiati (Egypt), Queso Blanco (South and Central America) andPaneer (India) are among the prominent cheeses mainly prepared from buffalo milk. In countrieswhere buffalo milk predominates, several cheese varieties are now manufactured from buffalomilk, which were earlier prepared from cow milk.25.2 Problems Associated with Cheese making from Buffalo MilkThe manufacture of cheese originated and flourished in countries with relatively cold climatewhere cows are the main milch animals. Consequently, methods of cheese manufacture weredeveloped for cow milk and emphasis was given to those varieties for which cow milk happens tobe most suitable. In contrast, in our country the major share of milk is from buffaloes. Buffalo milkis not considered suitable raw material for making certain ripened cheese varieties such asCheddar, Gouda, Emmental, etc.Ripened varieties are characterized by their soft, mellow and velvety body and texture and richpleasing flavor. The cheese made from buffalo milk results in flat flavor and hard, rubbery anddry body and texture. This is mainly because of the qualitative and quantitative differencesbetween cow milk and buffalo milk. Following phenomena are observed while manufacturingcheese from buffalo milk: Slower development of acidity Faster renneting time Lower retention of moisture in the curd Hard, rubbery and dry bodyThe high buffering capacity of buffalo milk, due to its higher calcium and casein content is thecause for slower development of acidity. Faster renneting time may be attributed to i ts highercolloidal calcium content (~160 mg/100 ml as compared to only 8 mg/100 ml cow milk). Lowerretention of moisture in the curd is the result of low hydration of its casein compared to cow milkcasein. Hard, rubbery and dry body may be due to high curd tension which, in turn, is the result94

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of the following: higher content of casein with bigger size of the micelles, high content of calcium and magnesium, more so in the colloidal state, larger proportion of solid fat with bigger size of globules and low voluminosity and solution of its casein micelles compared to the same in cow milk.Cheddar, the most common variety of cheese made in India does not develop proper flavor andbody and texture when it is made from buffalo milk. The major problem is considerably faster rateof renneting and syneresis, which result in lower retention of moisture in the finished product.This in turn, affects adversely, the three most important biochemical reactions, i.e. glycolysis,proteolysis and lipolysis which constitute the cornerstone of cheese flavor development.

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Lesson 26PROCESS MODIFICATIONS FOR BUFFALO MILK CHEESE26.1 Process Alterations to Prepare Quality Buffalo Milk Cheese26.1.1 Heat treatmentHeating buffalo milk at higher temperature is more suitable while preparing cheese from buffalomilk. The higher heat treatment results in partial precipitation of colloidal calcium and interactionof casein micelles with whey proteins prevents faster coagulation. The curd so formed retainsmore moisture, thereby improving body and texture of the resultant cheese.26.1.2 Ripening of milk (acidification)In case of cow milk about 1% active lactic culture is used for ripening of milk. A rise of 0.02%acidity in about 45-60 min is considered satisfactory for adding rennet. Since in case of buffalomilk acidity development is relatively slower due to its higher buffering capacity, the lactic cultureis added at the elevated level of about 2%.26.1.3 Supplementation of starter culture with starter adjunctsSupplementation of regular starter culture with Lactobacillus casei 300 or Lactobacillus helveticus atthe rate of 0.5% improves flavor development in buffalo milk cheese.26.1.4 Ripening temperature of milkRelatively lower temperature of ripening of milk (28C) in case of buffalo milk is more condu civefor acidity development as compared to the higher temperature (30C) in case of cow milk.26.1.5 Cooking temperatureRelatively lower cooking temperature in case of buffalo milk cheese (37C/40-45 min) is helpful inretention of greater amount of moisture as compared to cow milk cheese (39-40C/60 min).26.1.6 CheddaringDuring cheddaring, piling and re-piling of cheese blocks should be more frequent to ensuregreater retention of moisture in case of buffalo cheese.26.1.7 PressureLower pressure should be applied on cheese block in case of buffalo milk cheese as compared tocow milk cheese.26.1.8 Application of starter culture adjuncts and enzyme preparationIn order to accelerate the ripening of cheese further from buffalo milk application of starteradjuncts and exogenous enzyme preparations should be made.

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Module 12. Manufacture of processed cheese and related products

Lesson 27PROCESSED CHEESE AND RELATED PRODUCTS27.1 IntroductionProcessed cheese is a product made by blending natural cheese of different ages in requiredproportion with emulsifying salts followed by heating and continuous mixing to form ahomogeneous mass. Processed cheese was initially manufactured with the aim of increasing theshelf life of natural cheese. Manufacturing of process cheese involves blending of cheeses ofdifferent age. These allows sub-graded cheeses like gassy, highly acidic etc. to be utilized, insteadof those getting wasted.According to FSSR (2011), Processed Cheese means the product obtained by grinding, mixing,melting and emulsifying one or more varieties of cheeses with the aid of heat and emulsifyingagents. It may contain cream, butter, butter oil and other milk products subject to maximum 5.0per cent lactose content in the final product and edible common salt, vinegar/acetic acid, spicesand other vegetable seasoning and foods other than sugars properly cooked or prepared forflavoring and characterization of the product provided these additions do not exceed one sixth ofthe weight of the total solids of the final product on dry matter basis and cultures of harmlessbacteria and enzymes. It shall have pleasant taste and smell free from off flavor and rancidity. Itmay contain food additives permitted in the regulation and it shall conform to the microbiologicalrequirements as prescribed in the regulation. It shall have moisture not more than 47% and milkfat not less than 40% on dry matter basis.FSSR (2011) has defined Process Cheese Spread as the product obtained by grinding, mixing,melting and emulsifying one or more varieties of cheese with emulsifying agents with the aid ofheat. It may contain Cream, Butter oil and other dairy products, subject to a maximum limit of 5.0percent lactose in the final product, salt, vinegar, spices, condiments and seasonings, naturalcarbohydrate sweetening agents namely sucrose, dextrose, corn syrup, corn syrup solids, honey,maltose, malt syrup and hydrolysed lactose and food properly cooked or otherwise prepared forflavoring and characterization of the product provided these additions do not exceed one sixth ofthe weight of total solids of the final product on dry weight basis and cultures of harmless bacteriaand enzymes. It shall have pleasant taste and flavor free from off flavor and rancidity. It maycontain permitted food additives and shall conform to the microbiological requirements asprescribed in the regulation. It shall have moisture not more than 60% and milk fat not less than40% on dry matter basis.27.2 Classification of Processed Cheese ProductsAs per Code of Federal Regulations (CFR), USA, there are three main categories of process cheeseviz., pasteurized process cheese (PC), pasteurized process cheese food (PCF), and pasteurizedprocess cheese spread (PCS). Table 27.1 summarizes the compositional specifications (CFR, USand FSSR, India) and the major ingredients which are used in their preparation.

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Table 27.1 Categories of cheese and their specifications

27.3 Preparation of Process Cheese

The manufacturing of process cheese involves selection and computation of ingredients, theirblending and shredding, addition of emulsifying salts, heating, packaging, cooling and storage.27.3.1 Selection and computation of ingredientsIt involves selection of type of cheese and various ages of cheese, emulsifying salts, water andother optional ingredients to give process cheese the desired composition, textural and functionalproperties. The major constituent of process cheese is cheese. Types of cheese, degree of maturityand the blend selected for processed cheese have a major influence on textural attributes of thefinal product. Processed cheese can be made from only one or several types of cheeses. A blend ofcheese having varying degree of maturity is selected on the basis of required flavor and texture inthe finished product. General formulation of processed cheese is 70-75% mild cheese and 25-30%medium aged or mature cheese. For producing processed cheese in slices, Kosikowski hadsuggested a blend composition of 55% young, 35% medium aged and 10% aged cheese in order toobtain optimum firmness and slicing qualities.Use of higher proportion of young cheese results in lesser raw material cost, formation of a stableemulsion with high water binding properties, firm body and good slicing properties. Sometimes itmay also result in a product having mild taste, excessive swelling, and a tendency to hardenduring storage. Similarly, a high content of mature cheese have the advantages of full flavordevelopment and flow properties while the disadvantages may be the harsh (sharp) flavor, lowemulsion stability and a soft consistency.After selecting all the ingredients, the quantity of the ingredients is calculated on the basis of fatand dry matter content of the natural cheese components. Formulation of material balance of fatand dry matter including all the ingredients, water, and moisture loss during heating is made in a98

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way to yield the finished product with desired composition.

27.3.2 Shredding and mixingAfter calculating the quantities of all the ingredients, all types of cheese are shredded and eitherpre-mixed with other ingredients or mixed in the process cheese cooker before processing. Pre mixing of cheese with other ingredients offers some advantages like physico -chemical changes atlower temperature prior to cooking which results in more uniform quality in the end product.Since cheese of different ages is used in manufacturing process cheese, there may be batch-tobatch variation in the hydration time of cheese and the free fat emulsification. Pre -mixing evensout the effects of differences in processability of cheese of varying age on the consistency of thefinal product.27.3.3 Processing the blendFollowing pre-mixing, the blend is discharged into the cooker, where it is processed. When pre mixing is not practiced, the ingredients are added directly to the cooker. The ingredients areadded in the order of ground cheese, a dry blend of emulsifier and other dry optional ingredients,water and flavors. Emulsifying salt may also be added with a portion of water at the start ofcooking process. The remaining water may be added later in the processing stage. This ispracticed especially where cooking time is relatively short. Flavors may be added later in theprocess to minimize the loss of volatile flavor compounds.Processing refers to the heat treatment of blend by direct or indirect steam with constant agitation.The main functions of processing are killing of pathogenic and spoilage microorganisms to extendthe shelf life of the product and to induce physico-chemical and microstructural changes whichtransform the blend to an end product with the desired characteristics and physico -chemicalstability. Processing may be carried out in batch or continuous cookers. The time -temperaturecombination of processing varies depending on the formulation, the extent of agitation, and thedesired characteristics in the finished product.Batch Processing--- 70-95oC for 4-15 minContinuous Method140oC for 5-20 sIn continuous method, after giving the required heat treatment, it is essential to hold the productat around 70-90oC for 4-15 minutes for interaction of different ingredients and for desired physico chemical changes to occur. Processing may also be performed continuously using extrusioncookers at a temperature of about 70-90oC. Extrusion cooking gives a high degree of proteinhydration and rapid emulsification.27.3.4 HomogenisationThe processed hot mass may be homogenized in a two stage homogenizer at pressures of 15 and 5MPa, respectively. It improves the stability of the fat emulsion, consistency, structure, appearanceand flavor of the processed cheese.27.3.5 Hot packing and coolingHot processed cheese blend can be transported to packaging machines directly from cooker or abuffer tank can also be installed in between. Processed cheese is usually packed and wrapped in99

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lacquered foil, tubes, cups, cans and cardboard cartons. It may also be packed in the form of sliceswherein, the hot molten cheese is pumped continuously into an endless 'tube' of plastic film, e.g.saran-coated polyester, which is automatically flattened and crimped into a chain of individualwrapped slices using crimping conveyors and rotating crimping heads. The chain of slices is thenpassed through a water-cooling tank and cooled to <10C, dried by removing water using fansand/or scrapers, and finally cut into individual slices which are stacked and packed.The body of the finished product may vary from firm and sliceable to semi-soft and spreadable,depending on the blend formulation, processing conditions and the cooling rate. The product thatis cooled slowly develops a firmer body as compared to the product that is cooled faster. Thus, theprocess cheese should be cooled as slow as possible while in the case of process cheese spread fastcooling is required.27.3.6 StorageThe finished product is stored at less than 10 oC. It should not be stored under frozen conditions aslow temperature may induce crystal formation.

Fig 27.1 Flow diagram for manufacture of Processed cheese products

27.4 Cheese PowderCheese is dried to prolong the keeping quality and to reduce weight and bulk. Cheese powdersare used as functional and natural flavor ingredients in a wide range of food/culinaryapplications including biscuits, savory, snacks, soups, bakery, sauces, dressings, ready meals andprocessed cheese. Majority of hard cheeses can be transformed into powder. Among cheeseswhich are produced in powder form, Parmesan and Cheddar are the most common. There areseveral methods of dehydrating cheese. These include direct tray drying, roller or spray drying,extrusion drying and freeze drying. Among these methods, spray drying is most commonly used.The technological process of dried cheese production is different from that of majority of other dryproducts. Cheese is first ground, and stirred with intensive agitation while adding water at 2732C to achieve the dry matter concentration optimal for spray drying (35-45%). At this stage,

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melting salts, comprising sodium citrate, disodium phosphates or polyphosp hates are added toprevent milk fat separation. The well-mixed mass is pasteurized, heated to 60C andhomogenized. It is spray dried at about 175C inlet air temperature and immediately cooled to 2932C, then shifted and packed in bags. Packaging in the atmosphere of inert gas and addition ofantioxidants can extend the shelf life of dry cheese.

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Module 13. Defects in Cheese

LESSON 28DEFECTS IN CHEESE, CAUSES AND PREVENTIVE MEASURES28.1 Defects in Cheddar cheeseCheese is a product of fermentation and consequently undergoes constant changes. Itscharacteristics of flavor, body and texture, color and curing qualities are influenced by the qualityof milk, techniques of manufacture, temperature of curing and length of curing time. Cheesedevelops defects when there is deviation in the selection of appropriate quality of milk, method ofmanufacture and curing.Table 28.1 Defects in cheese can be related to the following aspects

28.2 Defects Related to Moisture Content

The presence of either too little or too much moisture in cheese is associated with certaincharacteristics. The qualities of cheese affected are flavor, body or consistency, texture or opennessand color. When the moisture is extremely high or low, the finish of the cheese is also affected.Moisture has an influence on all of these characteristics becau se it is directly related to thecomposition and physical qualities of the cheese. Moisture is indirectly related to thesecharacteristics because it carries lactose and some of the milk salts in solution. Microorganismschange lactose to acid, chiefly lactic. A certain amount of such lactic acid formation is necessaryfor proper cheese making and ripening; excessive amounts make the cheese taste sour whileinadequate amounts may delay ripening or may actually encourage abnormal fermentations ofundesirable type. The amount of moisture in cheese must be properly controlled.28.2.1 Excessive moisture102

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The characteristics of cheese with excessive moisture are as follow:

a) Flavor may be sour or acid or merely slightly acid when fresh, and lacking in cheese flavor andsour when aged.b) Body may be weak or soft when fresh, and sticky and pasty when aged.c) Texture may be open if the acid development during the making operation is inadequate.d) Color may be higher.28.2.1.1 CausesOne or more of the following may be responsible:

An unusually high fat content in milk fat delays firming.

Lack of acid development during making.

Insufficient heating or heating too rapidly.

Incomplete removal or elimination of whey.

28.2.1.2 PreventionIt is usually not necessary to apply all the measures of control indicated. The results mightproduce cheese with too little moisture. The corrections may be selected by scrutinizing themanufacturing records.28.2.2 Effects of insufficient moisturea) Flavor - mild or lacking. It may be slightly acid if lack of moisture was caused by excessive acidduring making. Cheese flavor develops slowly.b) Body - firm, hard or corky, and sometimes crumbly and mealy. Loss of curdy characteristicsduring ripening is extremely slow.c) Texture - usually close and solid but may show mechanical openness where curd particles failedto knit together properly during pressing.d) Color - sometimes deeper in shade and rind formation is frequently darker in color than the restof the cheese.e) Finish - may show defective knitting together of curd particles.28.2.2.1 CausesMay be due to one or more of the following:

Maximum acid development throughout making process.

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The use of excessive amounts of rennet or CaCl 2

Fine cutting or breaking of the curd.

Heating and holding temperature high.

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Excessive stirring of the curd while the whey is being removed and immediately afterdipping.

Lack of piling during cheddaring operation.

Addition of too much salt.

Holding the cheese in a warm drying room long before paraffining.

28.2.2.2 Preventiona) At saltingSteps may be taken to reduce the acid development, ripening period and amount of starter,besides adding the rennet sooner. The amount of rennet should be reduced, use of calciumchloride should be avoided, a firm cut should be developed at cutting and coarser knives may beused for cutting curd.b) At heatingThe temperature may be decreased. If the temperature used approximates 36C, then aciddevelopment may be stimulated.c) At dippingMinimum amount or acid recommended for normal making operation should be developed. Thecurd should be settled 30 min before dipping and it should not be stirred at any time thereafter.As the curd settles under the whey, it should be pushed towards the side of the vat to form layersapproximately 25 cm deep. The whey should be removed early and before the curd developsextreme firmness, this measure of control is most commonly used and is entirely adequate evenwhen applied alone in ordinary making practice. The layers of curd should be cut into blocks 25cm wide and piling should be sooner than usual. It should be piled 4 or 5 high before milling.Allow the curd to cool during cheddaring.d) At MillingUse the minimum acid development consistent with recommended making procedure. Cool thecurd promptly after milling by stirring and rinsing highly with water at 15-21C. Salt the curdpromptly and use the minimum amount indicated for normal cheese. After pressing remove thecheese to a cool room and paraffin it as soon as the rind is properly dried.28.3 Defects Related to Acid ContentThe presence of too much or too little acidity in Cheddar cheese is associated with certain defects.Excessive acidity is found in cheese that contains more than normal amounts of moisture becausesuch cheese contains more than normal amounts of lactose. Excessive acid development during104

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the making process can also produce acid defects in the finished cheese even when the moisturecontent of the product is normal or perhaps less than normal.28.3.1 Effects of excessive acidityAll the physical characteristics of Cheddar cheese may be affected by excessive acidity.a) Flavor acid or sour. Bitterness is sometimes associated with too much acid developmentduring making. True cheese flavor is lacking or slows in development.b) Body firm, dry, crumbly, short and mealy when the moisture content is low, it may be soft,pasty, sticky, and short when the moisture content is high.c) Texture usually close although in extreme instances the curd particles may be so poorlyknitted together that numerous mechanical openings will be formed.d) Color bleached or acid cut and sometimes mottled.e) pH usually less than 5.05 when the cheese is 3 to 4 days old.28.3.1.1 Causes Too much moisture in cheese High acid initial milk Use of too much starter Prolonged ripening period Too much acid development before adding rennet Too much acid development at other steps28.3.2 Effects of lack of AcidityThe common characteristics:a) Flavor - mild when fresh and fermented, fruity or lacking when aged. True cheese flavordevelops slowly, if at all.b) Body - corky, pasty, sticky or weak. The cheese remains curdy for long time in curing.c) Texture - open, with large mechanical holes. The cheese with insufficient acidity may also showthe effects of uncontrolled fermentations of gas producing yeasts or bacteria.d) pH - usually more than 5.3 when the cheese is approximately 4 days old.

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28.3.2.1 Causes

Failure of starter - due to inactive starter, improper handling of starter, unfavorable

At Milling - Delay milling until the whey draining from the curd shows at least 0.30% acid.The hot iron test should be nearly 3/8 long and the pH of the curd should be not morethan 5.6.

If the acidity of the whey after two hours of dipping does not exceed 0.25%, then it is highlyprobable that the starter is faulty or that it is contaminated with bacteriophage. If contaminatedwith phage, prolonging Cheddaring operations for 4-5 h do not help acid development. Holdingthe curd in pack for 12 h or longer sometimes permits acid development in curd affecte d withphage. The curd must be kept at 29C during this period.28.4 Defective flavors28.4.1 Acid flavorThis results from the development of too much acid at any stage of cheese making or curing. Itmay occur from high acid milk as received, ripening too long before setting, too much starter,improper cutting, cooking too fast or other factors which may interfere with proper expulsion ofwhey from the curd, or otherwise developing acid faster and higher than normal. Low salt contentof cheese may also be a contributing factor.28.4.2 Bitter flavorThis is a common defect. It is associated with inferior milk and poor starter, with excessivemoisture and high acidity in cheese and using too much rennet and unclean utensils. Relativelyhigher temperature and use of Leuconostoc sp. as starter has been noted to cause the defect.Unclean conditions e.g. rust spots, open seams, milk stones in cans and utensils may cause thisdefect. Conditions associated directly with the manufacturing operations may also be responsiblee.g. excess acid, excess moisture, lack of salt, and high curing temperature.28.4.3 Fermented flavorThese flavors are characteristics of the odor of fermented whey and possess some of the qualitiesof the combined odors of alcohol, acetic acid and propionic acid. They may appear in cheese soonafter it is made, but they usually develop after the cheese is two weeks old. They are believed to becaused by yeasts or bacteria. These organisms may get into the milk on the farms by contact withunclean and non-sterile surfaces of utensils, milking machines, and milk cans. This can beprevented by:(i) Utmost precaution in plant sanitation,(ii) Clean and active starter and(iii) Ripening at 7C or below.106

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28.4.5 Fruity flavor

The fruity flavor defect has been described as pineapple, raspberry or pear-like flavor in cheese.The compounds responsible for the defect are esters, certain acetaldehydes and ketones and somealcohols. This flavor defect is closely related to the fermented flavor defect. Hence the origin,prevention and remedies are identical to that of fermented flavor defect.28.4.6 Moldy flavorIt is associated with curing conditions. It is caused by the growth of mold in or on the cheese.Mold will grow in Cheddar cheese only when O2 gains entry through openings in the rind orthrough openings or cracks inside the cheese which connect with trier holes or other defects in therind.Mold grows slowly on cheese held at low temperature and under dry conditions; it grows rapidlyat high temperature and high humidity. It grows most luxuriantly on non-paraffined cheese.Prevention Proper paraffining, close texture, sound rind, curing at 7C and relative humiditybelow 75% minimize the defect.28.4.7 Rancid flavorRancidity is the flavor characteristic of the odor of butyric acid. It is believed to be present in allnormal Cheddar. This flavor may come from the milk itself.28.4.8 Unclean flavorFlavors that are foreign to milk and cheese but which can not be identified or otherwise describedare usually called unclean. Unclean flavors are often attributed to the development of undesirablemicroorganisms in the milk, curd or cheese.28.5 Defects Related to BodyThe term body is used by technologists in the cheese industry to designate the physical propertiesof consistency. These properties include firmness, cohesiveness, elasticity and plasticity. Thesephysical characteristics of cheese are sometimes called rheological properties. Firmness is theproperty of the cheese which causes it to resist deformation or distortion under pressure.Cohesiveness is the characteristics of the cheese that causes it to stick together. Elasticity is thecapability of the cheese to recover its size and shape after deformation. Plasticity is the quality ofthe cheese which enables it to be deformed under pressure without rupture.The rheological properties of cheese are affected by methods of manufacture and composition ofcheese.Various terms are used to indicate firmness, elasticity, cohesiveness, and plasticity of curd andcheese. These terms describe the appearance and feelings of the cheese when a plug is removedfrom the cheese block. A normal plug of ripened Cheddar cheese shows a smooth, uniformsurface. It feels solid and firm, it does not crumble, when cut or pressed. It bends before breakingand when rubbed between the thumb and fingers, it feels smooth and waxy like cold butter.Some of the common defects are as follow:

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28.5.1 CorkyCheese with a firm, hard, tough and somewhat elastic consistency is called corky. Such cheese isdifficult to crush with the fingers, but when enough pressure is applied it breaks apart in a woodymanner.Corky body may be apparent as very firm curd at the time of draining; the characteristics usuallyappear before salting. Corky characteristics may persist throughout the life of the cheese.Causes Low fat content, lack of acid development, over-heating during cooking, lack of moistureand excessive salt content.28.5.2 CrumblyThis defect is characterized by the falling apart of cheese when sliced, by difficulty in removing afull plug and by the breaking of the cheese into pieces that crumble when crushed between thethumb and fingers. This lack of cohesion is apparent through the whole cheese and is not li mitedto the surfaces of the curd particles which make up the cheese. Crumbly cheese usually feels firmbefore breaking. It shatters with a snap, like breaking of chalk.The defect rarely appears during the making operations, although the first stage of crumbly bodymay be evident when excessively acid curd fails to mat properly during cheddaring. The defect isusually apparent in fresh cheese within a week after making; it persists throughout the life of thecheese.Crumbly body in cheese can be prevented by observing the preventions and remedies forexcessive acidity.Crumbly body gradually develops in aged cheese and is not regarded as a defect, if the cheese issweet in flavor. This crumbly body is caused by ripening changes in the foods and by loss o fmoisture. This condition is associated only with a fully matured flavor in the cheese.28.5.3 CurdyThis characteristic is natural in fresh cheese and is rightly regarded as a defect only when itpersists beyond about 30 days. Curdy cheese, when broken apart, reveals the size and shape of theoriginal curd particles after salting.When pressed between the fingers it feels elastic, firm and somewhat like the particles of curd atthe time of salting. It cannot be worked together in the fingers after it has once been broken apart.28.5.3.1 Causes

Low moisture content which delays curing

Lack of proper acid development

Lack of proper cheddaring in the vat before milling

Addition of excessive amounts of salt, or

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Low temperature storage.

28.5.4 MealyThis characteristic appears when cheese is crushed and rubbed between the thumb and fingers,the structure of the curd looks and feels rough, the characteristic is the opposite of the waxy,smoothness desired in normal cheese.Mealy body can be most readily detected after the curdy characteristics of the cheese have fullydisappeared; it is actually apparent during the first week of curing but is not so easily discovered.It persists throughout the life of cheese.Cause - Excessive acidity, it may be regarded as a stage of disintegration of crumbly cheese.Mealy body in cheese can be eliminated in future lots by observing the preventions and remediesfor excessive acidity.28.5.5 PastyCheese with this defect is soft in consistency, when pressed and rubbed between the fingers, itquickly becomes sticky and clings to the fingers.Pasty body in cheese becomes apparent as soon as the curdy characteristics disappear. The defectis caused by excessive moisture.28.6 Defects Related to TextureOpen texture is the most common defect in cheese. It may be due to the formation of gas ormechanical faults. The causes of this defect are as follows:a) Contamination of cheese with gas producing bacteria and yeasts.b) Lack of acidityc) Moisture contentd) Free whey trapped in curd, ande) Lack of sufficient pressure during pressing of cheese.The defect can be controlled by eliminating source of contamination, using pure culture, andpasteurizing the milk efficiently. Acidity of 0.16% LA at draining, piling hi gh, milling at acidity0.60% LA, delayed salting; washing the curd with water at 30C and curing below 10C also helpin controlling the defect.

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Cheese TechnologyTable 28.2 Color defects in cheese

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Module 14. Packaging, storage and distribution of cheese

Lesson 29PACKAGING OF CHEESE29.1 IntroductionPackaging refers to putting a commodity into a protective wrapper or container for shipment orstorage. Any material to be used for packaging natural cheeses must:a) afford general protectionb) prevent moisture lossc) improve appearanced) protect against micro-organisms ande) prevent oxygen transmissionPackaging of cheese is mainly done to protect the cheese at the time of storage and transportation.Traditionally, cloth was used with wood to give support and protection, but the invention ofpolymers or plastics has revolutionized cheese packaging. Cheese manufacturing is now-a-dayshighly mechanized and at the same time, many developments are taking place in the area ofcheese packaging also.Cheese is packaged mainly in two forms:a) Packaging cheese for storage and ripening (bulk packaging)b) Packaging for consumers (retail packaging)29.2 Bulk Packaging of CheeseFor bulk packaging of cheese, it is either paraffined or vacuum packed in flexible film. For waxing,the cheese can be lifted by means of suction and half immersed in wax and then other half can beimmersed. For vacuum packaging, there are now available vacuum packaging machines, gasflushing machines, over wrapping machines and vacuum skin packaging machines. Paraffining isnow completely replaced by film packaging as it causes considerable loss of cheese whileremoving paraffin. Many cheap and easy-to-apply films are now available.29.3 Modern Packaging Materials and Formsa) Materialsthe basic ones are paper (usually coated or lined), parchment, foil (usuallyaluminum), polythene, propylene, treated cellulose and cellulose acetate (e.g. cellophane),

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polystyrene, polyester, polyamide (nylon), rubber hydrochloride (e.g. cryovac) and Saran (a mixedpolymer). Laminates are now more common.b) Forms - wrappers, cartons, bags, tubes, tubs, jars, cans, etc.29.3.1 Film packagingThis has become synonymous with rindless cheese. In the latter, green cheeses of uniform sizeand shape are ripened in bags made of plastic films. The wrapped cheese may be placed in awooden box or jig to preserve its shape. If the cheese is made and ripened in the conventionalway, it may be cut into retail portions and wrapped by such method as the cryovac.Desirable properties of films for packaginga) The film must be strong so that it does not tear or change its property when rubbed against asharp point.b) It should be easily applied and sealed.c) It must be impervious to water vapor and oxygen.d) When the film is in contact with cheese, it should not change its inherent properties.e) The material must be chemically inert and non-toxic for humans.Plastic film packaging of cheese is applicable to varieties except such extreme types as cottage(which has very high moisture content) and as Parmesan (which is very low in moisture). Thereare many advantages and few disadvantages of film packaging which are summarized as follows:29.3.1.1 Meritsi) It affords a considerable saving in labor.ii) It protects the cheese from attacks by molds, insects, rodents and fault-inducingmicroorganisms.iii) It is easily applied and the method can be readily mechanized.iv) There is practically no loss of moisture and of weight in the cured cheese (In traditionalripening the loss may be 3 to 7%, even up to 12 %)v) The method permits and is suitable for packaging small quantities, which make handling andretail trade easier.vi) The method is most easily used for rectangular blocks.vii) It is cheap and convenient.viii) Humidity control is unnecessary during ripening and storage.ix) More cheese can be stored in a given volume.112

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x) Turning is unnecessary during ripening.

xi) It permits rindless curing so that whole of the cheese can be eaten. (When rind is formed as intraditional method, the loss can be as high as 10%).29.3.1.2 Demeritsi) Not all technical problems in film packaging have been solved. (For example, failure to obtain aperfect seal and to remove all air may result in mould growth).ii) The moisture content of the cheese at packaging must be less than for traditional packaging andmust be carefully standardized. Failure to do so may lead to the growth of taint-producingorganisms.iii) The ripening process in some cheeses (such as Camembert) may be affected.iv) The film does not always give the same mechanical protection to cheese as traditional methods.v) The most careful attention to detail is necessary in film packaging.29.4 Retail Packaging of CheeseRetail packaging is an important aspect which affects not only the shelf life of cheese but also itsmarketability. Cheese is available in the form of slices, cubes, tubs, paper board cartons with foiloverwraps, etc. These are available in different retail sizes like 100 g, 200 g etc. With thedevelopments taking place in packaging technology, cheese packaging is also revolutionized.Active packaging and modified atmosphere packaging is being used for retail cheese packaging.29.5 Developments in Packaging of Different Types of Cheese29.5.1 Soft cheeseSpecial packaging requirementsThe packaging material requirements for soft cheeses differ considerably depending on whetherthe cheese concerned is a soft cheese with a mold formation (surface mold, Camembert), blueveined cheese (Roquefort), or a so-called smeared cheese (Munster). Different bacteria and moldflora require packaging material to have specific properties.29.5.2 Fresh CheeseSpecial packaging requirements29.5.2.1 Protection against lightMetals are impervious to light. With regard to fresh cheese packaging this concerns first andforemost aluminium, whether in the form of lids to seal plastic containers or as deep -drawncontainers. A high degree of imperviousness to light can be achieved through the addition ofcarbon black or brown pigments (total transmission approaching 0%). As black cheese packagingwould not be acceptable to the consumer, such light-preventing layers are usually produced as theinner sheet of multilayer films by co-extrusion. This has not been done in dairy industry because113

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of cost. The outstanding barrier property of aluminium is also found with vacuum metalizedplastic films (e.g. polyethylene terephthalate polyester (PETP), oriented polypropylene (OPP),cellophane or paper).29.5.2.2 Protection against the effects of oxygenIn order to avoid the diffusion of oxygen, especially in packed fresh cheese with a long shelf-life,the most impervious packaging material possible must be selected. This is achieved using Al (foilor strips), metalized plastics or by means of O 2 resistant layers in plastic combinations such aspolyvinylidene chloride (PVDC), ethylene vinyl alcohol (EVAL) or polyvinyl alcohol (PVAL).When selecting mono or multilayer combinations (bags or thermoformed containers) it should beborne in mind that the data concerning gas permeability always refers to flat (unfolded) material,measured at +23oC. When a pack is formed, the permeability may change significantly due tocapillarity in the sealed seam, thinning of the material at the base of deep -drawn containers orfractures caused by bending in bags.29.5.2.3 Protection against loss of moistureThe absorption of moisture is not of any significance for packaged fresh cheese. On the otherhand, however, fresh cheese with a long shelf-life must be protected against loss of moisture. Inaddition to the specific properties of water vapor permeability of the various packaging materials,the way they are processed into finished packs is also important.29.5.2.4 Protection against contaminationQuite apart from contamination through leaks in the packs or lids, the packaging material itselfmay be contaminated to a greater or lesser extent. Paper which is used as wrappers may beaffected as a raw material or during production by bacteria and/or mould conidia.Due to high temperatures involved in processing, plastics are considered virtually bacteria-free.However, the possibility of contamination from the environment cannot be ruled out duringfurther converting into film and containers.29.5.3 Hard cheese29.5.3.1 Emmental cheeseA pressed, block-shaped Emmental Cheese (84 kg) is wrapped in cling film and stacked on aspecially designed pallet, which can be mechanically turned during the ripening/storage period.The smaller block-shaped Emmental could be packaged mechanically in a Cryovac-BKIL bag.This type of packaging material is a laminate of different layers of plastics.29.5.3.2 Cheddar and related cheese varietiesDifferent systems have been employed for the packaging of Cheddar Cheese and other Britishvarieties. These may include the following:a) PukkafilmThis type of packaging material consists of a waxed cellulose laminate. First, the cheese block is

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wrapped with the laminate; secondly, it is over-wrapped with waxed cellulose; and thirdly thecheese is placed in a chamber for sealing by the application of heat and pressure.b) Unibloc systemThe pressed cheese is wrapped with a plastic film, e.g. Saran and over-wrapped with a layer ofpaper prior to packaging within six wooden slats. The cheese is compressed within the slats by aspecially designed machine, and the pressure is maintained by placing four metal straps aroundcheese. In some instances, the wrapped cheese is placed within a thin cardboard box before finalpackaging. This box serves as a dispatch unit when the cheese leaves the factory, and the woodedslats are retained on the premises.c) StorpacThe packaged cheese, e.g. in a vacuum pouch or heat-shrink bag is wrapped in a thin cardboardbox (optimal) and is placed in a wooded box with a loose cover. The latter piece is held onto thebox using a plastic band for strapping. On dispatch the strap is removed from these boxes whichare retained in the factory.d) Heat-shrink bagsAn example of such a bag is the Cryovac-BB4L bag, which consists of three main layers:polyolefine, a PVDC barrier layer against oxygen and moisture and a cross-linked polyolefine. Gasproduction in Cheddar cheese during the maturation period is considered a serious problem, anda quick remedy is to package the cheese in carbon dioxide permeable material, e.g. Cryovac-BKILbag.e) Vacuum pouchDifferent types of plastic film laminates can be used to package Cheddar cheese, and such pouchesshould provide a barrier against oxygen ingress and moisture loss. One such example is theDiolon pouch which consists of 20 m nylon (polyamide) and 60 m polyethylene.29.5.3.3 Gouda, Edam and related cheesesAfter brining stage, the cheese is plasticized twice to prevent mould growth during the ripeningperiod, and this process is repeated several times if the cheese is to be stored for long periods.Prior to dispatch, the cheese is washed, dried and coated with paraffin wax and over-wrappedwith a red cellophane film (the latter packaging material is optional). The mechanical handling ofcheese in the store and the waxing equipment are of great concern.An alternative approach for the packaging of the loaf, block or round Dutch cheeses is to wrapthe product in a heat-shrink bag, which is then either sealed by heat with a metal clip.However, recent reports indicate that the protective packaging of foods is not available in a singlepackaging material if the desired shelf-life has to be achieved. Various packaging materials areused in combination to give the desired shelf-life of cheese. Plastic combinations, Al-foil/paperlaminates, cellophane/paper combinations, etc. are in use these days. Modified AtmospherePackaging has contributed greatly great to increase the packaging speed and thus reduce the cost.Still cheaper combination packages and modern methods are in demand mainly as consumerpackages with all the desirable properties.115

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Lesson 30STORAGE AND DISTRIBUTION OF CHEESE30.1 IntroductionAfter completion of the post-processing treatments like bandaging and dressing, the cheeses arekept in the ripening room. This starts the process of ripening. For some varieties of cheese likeCheddar and Parmesan, ripening and storage are the same while for others like Camembert andRoquefort, ripening and storage are two different processes as they need altered temperature andhumidity in both the processes. Storage is inevitably, a continuation of the ripening process(except changing temperature and humidity for some varieties) so that all the considerationswhich apply to the ripening period apply equally to the storage period.30.2 Shelves for Ripening/Storage of CheeseIn traditional practice, wood was used as the material for construction of shelves. But it has manydisadvantages like it gives shelter to pests and is an excellent medium for the growth of moldsand other microorganisms, once it is wet. So, wooden shelves need lot of care and maintenance.The easiest materials to clean are glass and stainless steel.30.3 Factors Affecting Ripening and StorageThe two most important factors controlling ripening and storage are temperature and humidity.Thus the ripening or storage rooms should have means for controlling these two factors.30.3.1 TemperatureIt is necessary to control the temperature during storage and maintain uniform temperature asalmost all biochemical reactions are temperature-dependent. Higher temperature acceleratesripening but jeopardizes the quality of cheese as it results in the growth of undesirablemicroorganisms. For cheeses of Cheddar and related varieties, temperature of 5-7C is ideal but 812C is considered economically best. Temperature higher than 18C should be strictly avoided.30.3.2 HumidityThe relative humidity of a gas is the amount of water vapour present expressed as percentage ofthat required to saturate the gas. Higher humidity leads to mold growth, accelerated ripening andsurface bacterial taints. Lower humidity results in cracking, shrinking, distortion and retardationof ripening in addition to excessive loss of weight. The correct humidity for ripening depends onthe type of cheese. Soft cheese requires a higher humidity (95%) than open-textured hard cheese(85%) and these again require greater humidity than close-textured hard cheese (80%). Further,mold ripened cheese require higher humidity than other varieties of cheese.30.4 Storage Conditions for some of the Cheese VarietiesCheeses of the Cheddar family (Cheddar, Cheshire, etc.) are ripened at lower temperatures ofabout 4-8C, and a relative humidity (RH) lower than 80%. The ripening time may vary from a116

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few months up to 810 months or even 12 months.

Other types of cheese like Emmental are first stored in a green cheese room at 812C for some 34 weeks followed by storage in a fermenting room at 2225C for some 67 weeks. After that thecheese is stored for several months in a ripening store at 812C. The relative humidity in allrooms is normally 8590%.Smear-treated types of cheese Tilsiter, Havarti and others are typically stored in a fermentingroom for some 2 weeks at 1416C and a RH of about 90%, during which time the surface issmeared with a special cultured smear mixed with a salt solution. Once the desired layer of smearhas developed, the cheese is normally transferred to the ripening room at a temperature of 1012C and a RH of 90% for a further 23 weeks. Eventually, after the smear is washed off andcheese is wrapped in aluminium foil, it is transferred to a cold store, 610C and about 7075%RH, where it remains until distributed.Other hard and semi-hard types of cheese, Gouda, Edam, may first be stored for a couple of weeksin a green cheese room at 1012C and a RH of some 75%. After that a ripening period of about34 weeks may follow at 1218C and 7580% RH. Finally the cheese is transferred to a storageroom at about 1012C and a relative humidity of about 75%, where the final characteristics aredeveloped.30.5 Factors Controlling the Loss of Moisture in CheeseThe primary factors which control the loss of moisture in cheese are temperature, moisturecontent, size and shape of the cheese and RH of air. The rate of loss of moisture rises sharply withtemperature. With storage at 5, 10 and 15C, the losses in 6 months were found to be 4.4, 6.4 and8.7%, respectively. Higher the moisture content, higher will be the rate of loss and more is the freemoisture. The smaller the cheese, the more rapid the losses of moisture as a proportion of thatinitially present. The higher the RH of the air in the cheese storage room, slower will be the rate ofmoisture loss.Other factors that influence the loss of moisture during storage are type and quality of the wax orfilm applied to the outside of the cheese and type of cheese.30.6 Distribution of CheeseDistribution of cheese from manufacturer to distributor/retailer should be done under strictconditions of appropriate temperature. For cheese varieties, which continue to ripen in the storageperiod, it is important to maintain the temperature for ripening during distribution also. Forexample, Cheddar cheese should be distributed at the temperature of 5-8C. Refrigerated andinsulated vehicles are used for this purpose.

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Module 15. Accelerated ripening of cheese

Lesson 31ACCELERATED RIPENING31.1 IntroductionThe ripening of cheese is a complex process of concerted biochemical changes, during which abland curd is converted into a mature cheese having the flavor, texture and aroma characteristicsof the intended variety. Ripening is an expensive and time-consuming process, depending on thevariety, e.g. Cheddar cheese is typically ripened for 6-9 months while Parmesan is usually ripenedfor two years. Extended ripening period involves increased cost due to refrigerated storage, space,labour apart from considerable loss in weight and higher capital cost. Acceleration of cheeseripening can also be a means of increasing the production of cheese in developing countries whereinvestment in storage facility can be a limiting factor.31.2 Accelerated Ripening of CheeseCheese ripening is essentially a process which involves metabolism of key constituents of milk, i.e.lactose, proteins and fat. Most of the lactose is lost in whey but the residual lactose is quicklymetabolized to lactate by combined action of starter bacteria and native bacteria of milk. Thislactate serves as an important precursor compound for certain reactions which occur duringripening. Citric acid fermentation also plays a role in cheese ripening. Milk contains very low levelof citrate, most of which is lost in whey. However, the residual citrate in the curd is acted upon bycitrate fermenting microorganisms like Leuconostoc sp. to produce important flavor compoundslike diacetyl, acetoin, etc. Lipolysis of milk fat is vital for production of important flavorcompounds. Milk fat is hydrolysed during ripening by the action of enzymes. These enzymes mayoriginate from milk like lipase or they may come through coagulant like rennin or they may beproduced by cheese microflora. Lipolysis converts milk fat into free fatty acids and glycerol. Freefatty acids, particularly short chain fatty acids, contribute directly to cheese flavor and they alsoact as precursors for various catabolic reactions including esterification of hydroxyacids to formlactones, formation of thioesters by reaction with sulphydryl compounds and -oxidation of fattyacids to alkan-2-ones. Other principal metabolism during cheese ripening is proteolysis, whereinprotein is broken down to peptides by the action of residual coagulant and the principalindigenous proteinase in milk, plasmin. These peptides are then hydrolyzed by enzymes derivedby starter and non-starter microflora of the cheese. The production of small peptides and aminoacids is caused by the action of microbial proteinases and peptidases respectively. The finalproducts of proteolysis are amino acids, the concentration of which depends on the cheese variety.All these biochemical changes which occur during ripening are slow and take abou t 6 months toyears, depending on the variety of cheese. For example, Cheddar cheese is typically ripened for 6 9 months while Parmesan is usually ripened for two years. Such extended period of ripeninginvolves capital investment in form of product and utilities like storage rooms, refrigeration etc.Therefore, various technological interventions are applied to shorten ripening period. This processof reducing normal ripening period is called as accelerated ripening.

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31.3 Methods of Accelerated Ripening

Ripening is a slow and consequently, expensive process that is not fully predictable orcontrollable. Therefore, there are economic and possibly technological incentives to accelerateripening. The principal methods by which this may be achieved are: an elevated ripeningtemperature, exogenous enzymes, modified starters and adjunct cultures. At least some of themethods used to accelerate ripening may also be used to modify flavor and in effect to create newvarieties/ variants. Slow flavor development and low flavor intensity are major problems withreduced-fat cheese and the methods used to accelerate ripening in general are applicable to lowfat cheese also. Several promising developments have emerged for rapid flavor development inCheddar cheese and other varieties.In this regard, various approaches have been used to accelerate cheese ripening process whichinclude: Use of elevated temperatures of ripening Addition of exogenous enzymes Use of adjunct cultures Genetic modification of starter bacteria Use of high pressure treatment31.3.1 Use of elevated temperatures of ripeningCheese is ripened at uniform temperature and humidity, depending on the variety of cheese.Ripening temperatures of some of the varieties of cheeses are as follows: Emmental, 22-24C (forpart of ripening, i.e., the critical hot room period); mold and smear-ripened cheeses, 12-15C;Dutch varieties, 12-14C; and Cheddar, 6-8C (the ripening temperature for Cheddar isexceptionally low). The above temperatures are the maximum in the profiles and are usuallymaintained for 4-6 weeks to induce the growth of a desired secondary microflora. Thereafter, thecheese is transferred to a much lower temperature (e.g. 4C). Cheddar is an exception, since it isnormally kept at 6-8C throughout the ripening process. It can be observed from the ripeningtemperatures of most of the varieties that in no case it is more than 20-25C as keeping cheeseabove this temperature causes texture to be too soft and the cheese deforms readil y. It may alsocause exudation of fat and excessive loss of moisture. Thus, the scope for accelerating the ripeningof most cheese varieties by increasing the ripening temperature is quite limited except forCheddar cheese which is ripened at low temperature of 6-8C. This is again limited to cheesewhich is made from good quality pasteurized milk and is microbiologically safe. This approach isthe simplest and cheapest method for accelerating ripening as no additional costs are involvedrather there may be savings due to reduced refrigeration costs.Several studies have been carried out to ripen Cheddar cheese at elevated temperatures. Forexample, the duration of ripening can be reduced by 50% by increasing the ripening temperaturefrom 6C to 13C, without adverse effects. The highest temperature that can be used continuouslyis about 16C, although 20C could be used for a short period; 12-14C is probably optimal.Ripening can be accelerated or delayed by raising or reducing the temperature at any stage duringthe process.119

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31.3.2 Addition of exogenous enzymes

Cheese ripening is essentially an enzymatic process and hence it should be possible to accelerateripening by augmenting the activity of key enzymes. However, addition of single enzyme, whichaccelerates one particular reaction, is unlikely to produce a balanced flavor. Hence, the need foraddition of mixture of enzymes in proper ratio has been advocated by several research workers.The addition of combinations of various fungal proteases and lipases to Cheddar cheese has beenreported to reduce ripening time by 50%. Lipase in combination with proteinase gave good cheeseflavor with low levels of bitterness. A lipase/proteinase preparation derived from Aspergillusoryzae released C6 -C10 fatty acids to produce typical Cheddar cheese flavor. To achieve moreintense and balanced flavor in buffalo milk Cheddar cheese, use of mixture 0.001% lipase and0.01% protease has been advocated. A number of options are available, ranging from the quiteconservative to the more exotic.31.3.2.1 CoagulantThe proteinases in the coagulant is principally responsible for primary proteolysis in most cheesevarieties and it might, therefore, be expected that ripening could be accelerated by increasing thelevel or activity of rennet in the cheese curd. Although, it is suggested that chymosin is thelimiting proteolytic agent in the initial production of amino nitrogen in cheese, several studieshave shown that increasing the level of rennet in cheese curd (achieved by various means) doesnot accelerate ripening and in fact probably causes bitterness. Chymosin produces only relativelylarge oligopeptides which lack a typical cheese-like flavor and may be bitter. Chymosin-producedpeptides are hydrolysed by bacterial (starter and non-starter) proteinases and peptidases andhence it would seem that increased chymosin activity should be coupled with increased starterproteinase and peptidase activities in order to accelerate ripening.Chymosin has very little activity on -casein in cheese, probably because the principal chymosinsusceptible bond in -casein, Leu192-Tyr193, is in the hydrophobic C-terminal region of themolecule which appears to interact hydrophobically in cheese, rendering this bond inaccessible.However, Cryphonectria parasitica proteinase preferentially hydrolyses -casein in cheese(possibly because its preferred cleavage sites are in the hydrophilic N-terminal region) withoutcausing flavor defects. Rennet containing chymosin and Cryphonectria parasitica proteinasemight be useful for accelerating ripening.31.3.2.2 PlasminPlasmin contributes to proteolysis in cheese, especially in high-cooked varieties in whichchymosin is extensively or totally inactivated. Plasmin is associated with the casein micell es inmilk, which can bind at least 10 times the amount of plasmin normally present, and is totally anduniformly incorporated into cheese curd, thus overcoming one of the major problems encounteredwith the use of exogenous proteinases to accelerate cheese ripening. Addition of exogenousplasmin to cheese milk accelerates the ripening of cheese made therefrom, without off-flavordevelopment.31.3.2.3 Other proteinasesThe possibility of accelerating ripening through the use of exogenous (non-rennet) proteinases hasattracted considerable attention over the past 20 years. The principal problems associated with thisapproach are ensuring uniform distribution of the enzyme in the curd and the prohibition of120

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exogenous enzymes in many countries. The earliest reports on the use of exogenous enzymes toaccelerate the ripening of Cheddar cheese appear to be those of Kosikowski and collaborators whoinvestigated various combinations of commercially available acid and neutral proteinases, lipases,decarboxylases and -galactosidase. Acid proteinases caused pronounced bitterness but theaddition of certain neutral proteinases and peptidases with the salt gave a marked increase inflavor after one month at 20C but an overripe, burnt flavor and free fluid were evident after onemonth at 32C. Incorporation of the enzyme-treated cheese in processed cheese gave a markedincrease in Cheddar flavor at 10% addition and a very sharp flavor at 20%. Good quality mediumsharp Cheddar could be produced in 3 months at 10C through the addition of combinations ofselected proteinases and lipases.With the exception of rennet and plasmin (which adsorbs on casein micelles), the incorporationand uniform distribution of exogenous proteinases throughout the cheese matrix poses severalproblems: Proteinases are usually water-soluble, and when added to cheese milk, most of the enzyme islost in the whey, which increases cost Enzyme-contaminated whey must be heat-treated if the whey proteins are recovered for use asfunctional proteins. The choice of enzyme is limited to those that are inactivated at temperaturesbelow those that cause thermal denaturation of whey proteins The amount of Neutrase that should be added to milk to ensure a sufficient level of enzyme inthe curd reduces the rennet coagulation time, yields a soft curd in which at least 20% of the casein is hydrolyzed at pressing and reduces cheese yield.31.3.2.4 Exogenous LipasesLipolysis is a major contributor, directly or indirectly, to flavor development in stro ng-flavoredcheeses, e.g. hard Italian, Blue varieties, Feta. Rennet paste or crude preparations of pre -gastricesterase (PGE) are normally used in the production of Italian cheeses. Rhizomucor miehei lipasemay be used for Italian cheeses, although it is less effective than PGE; lipases from Penicilliumroqueforti and Penicillium candidum may also be satisfactory. The ripening of blue cheese may beaccelerated and quality improved by added lipases. A blue cheese substitute for use as aningredient for salad dressings and cheese dips can be produced from fat-curd blends by treatmentwith fungal lipases and P. roqueforti spores. Although Cheddar- and Dutch-type cheeses undergolittle lipolysis during ripening, it has been claimed that addition of PGE or gastric lipase improvesthe flavor of Cheddar cheese, especially that made from pasteurized milk.31.3.2.5 -Galactosidase (Lactase)-galactosidase (lactase) hydrolyses lactose to glucose and galactose, results in stimulation oflactococci and shortens the lag period of growth of lactococci. Lactose hydrolysed cow and buffalocheese milks have been reported to reduce manufacturing time, improve flavor and accelerateripening. It has been found that the lactase from Kluyveromyces lactis available as Maxilact containsa proteinase, which is responsible for increased levels of peptides, and free amino acids.31.3.3 Use of adjunct culturesAdjunct cultures are specifically selected strains, which are intentionally added to accelerateripening of full fat cheese and for flavor enhancement of low fat cheese. Adjunct cultures121

different Lactobacillus spp. (L. casei and L. plantarum) to Cheddar cheese milk to a level of 105 106 cfu/ml increased the levels of free amino acids to attain highest flavor scores. Augmentation ofstarter culture with L. casei had definite and positive influence on the flavor; body and texture ofbuffalo milk Cheddar cheese. The flavor development and biochemical changes in buffalo milkCheddar cheese is faster when L. casei is supplemented with cheese.The principal adjuncts used in accelerated ripening of cheese are mesophilic lactobacilli andthermophilic lactobacilli. Inoculation with mesophilic Lactobacillus adjuncts enhanced flavor andaccelerated proteolysis at the level of small peptides and amino acids. Essentially the samevolatiles were produced in all cheeses but at very different concentrations. Mesophilic lactobacillimodify proteolysis; in particular, they result in a higher concentration of free amino acids andimprove the sensoric quality. In contrast to mesophilic lactobacilli, thermophilic lactobacilli dierapidly in cheese, lyse, and release their intracellular enzymes. Consequently, cheeses made withthermophilic Lactobacillus spp. as starters contain high concentrations of amino acids (theconcentrations are particularly high in Parmesan cheese). Although thermophilic lactobacilli willnot grow in Cheddar cheese, their inclusion as a starter adjunct markedly intensifies the flavor ofCheddar. Adjuncts of thermophilic lactobacilli and Streptococcus thermophilus are availablecommercially.31.3.4 Modification of starter bacteria/Starter cultures31.3.4.1 Genetically engineered startersFood-grade controlled lysis of Lactococcus lactis for accelerated cheese ripening is an importantapproach. An attractive approach to accelerate cheese ripening is to induce lysis of Lc. lactis starterstrains for facilitated release of intracellular enzymes involved in flavor formation. Controlledexpression of the lytic genes lytA and lytH, which encode the lysin and the holin proteins of thelactococcal bacteriophage phi-US3 , respectively, was accomplished by application of a food-gradenisin-inducible expression system. Simultaneous production of lysin and holin is essential toobtain efficient lysis and concomitant release of intracellular enzymes as exemplified by completerelease of the debittering intracellular aminopeptidase N. Production of holin alone leads topartial lysis of the host cells, whereas production of lysin alone does not cause significant lysis.Model cheese experiments in which the inducible holin-lysin overproducing strain was usedshowed a fourfold increase in release of l-Lactate dehydrogenase activity into the curd relative tothe control strain and the holin-overproducing strain, demonstrating the suitability of the systemfor cheese applications.31.3.4.2 Stimulation of starter cellsThe growth of starter cells may be stimulated by the addition of enzymes or hydrolysed startercells to cheese milk. Ripening of Emmental type cheese has been accelerated by using startersgrown to high cell numbers in media supplemented with protein hydrolysates andmetalloproteinase from Micrococcus caseolyticus.31.3.4.3 Modified starter culturesAddition of modified/attenuated starter culture is to increase the number of starter cells withoutcausing detrimental effect on the acidification schedule during manufacture, so that the cellscontribute only to proteolysis and other changes during ripening. Modified starter cultures withattenuated acid producing abilities are added with normal starter cultures during cheese122

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manufacture. Selection of starter strains with enhanced autolytic properties and increasedpeptidase activity would provide a more balanced flavor.31.3.4.4 Heat and freeze shock treated cellsMixed strain starters or L. helveticus culture subjected to various heat-shock treatments in anattempt to reduce their acid producing ability but to enhance their rate of autolysis. Some workersused heat-shock cultures to attain large number of a mixed-strain starter, containing Lactococcus,Leuconostoc or L. helveticus strains which were cultivated at a constant pH, followed by heating to69C/15 s. Flavor scores increased with increasing numbers of heat-shocked cells reducing theripening time to 50%. A combination of neutral proteinase with heat shocked L. helveticus to a finallevel of 4 x 106 cfu/g curd also accelerated the ripening of the cheese. Addition of heat-shockedlactobacilli increased peptidolysis and produced good flavor in low-fat semi-hard cheese. Flavoracceleration could be significantly improved by augmentation of starter culture with freeze shocked L. helveticus in buffalo Gouda cheese. The combination of liposome entrapped proteinaseand freeze-shocked lactobacilli resulted in development of more intense flavor without bitternessin UF cheese.The acid-producing ability of lactic acid bacteria can be markedly reduced by a sub-lethal heattreatment while only slightly reducing enzyme activities. Heating at 59 or 69C for 15 s wasoptimal for mixed mesophilic and thermophilic lactobacilli cultures, respectively. Most (90%) ofthe heat-shocked cells added to cheese milk at a level of 2% (v/v) were entrapped in the curd butentrapment efficiency decreased at higher levels. Proteolysis in Swedish cheese was increased andquality improved by addition of the heat-shocked cells to the cheese milk, L. helveticus being themost effective. The extent of proteolysis increased pro rata the level of heat-shocked L.helveticus cells added but not for the mesophilic culture. Bitterness was not observed in any of thecheeses. Heat-shocked (67C/10 s) L. helveticus cells accelerated amino nitrogen formation andenhanced flavor development in Swedish hard cheese; when added alone, Neutrase acceleratedproteolysis but it caused bitterness which was eliminated when both heat-shocked L.helveticuscells and Neutrase were added to the curd.31.3.4.5 Lysozyme treated cellsAddition of lysozyme-sensitised cells to cheese milk at a level of equivalent to 10 10 cells/g ofcheese indicated that intracellular dipeptidases were released and as a result, concentration of freeamino acids significantly increased. However, there was no effect on the rate of flavordevelopment. Economically, the use of lysozyme treated cells may not be viable for large -scalecheese manufacture owing to the cost of the enzyme. Addition of lysozyme encapsulated in adextran matrix to cheese milk at renneting, which would be released at Cheddar cheese pH (5.25.4) leading to the lysis of the cells with release of intracellular peptidases has also been suggested.31.3.4.6 Mutant starter culturesBecause the rate of acid development is a critical factor in cheese manufacture, the amount ofnormal starter cannot be increased without producing an atypical cheese. This has led to the use oflactose negative mutants, which do not affect the rate of acid development but provi de additionalenzymes. Like attenuated cells, these mutant cells serve as packets of enzymes but are much easierto prepare and would appear to be the logical choice when it is desired to increase the number ofcells without a concomitant increase in the rate of acid production. Lac- mutants of starter strainshave been reported to provide packets of uniformly distributed proteinases/peptidases,enhancing the production of peptides and free amino acids without interfering with acid123

lactis subsp. cremoris (Lac Prt-) cells received highest flavor scores. Some workers have showedadvancement in ripening of 4-12 weeks after 6 months storage in Cheddar cheese with mutantstarter.It was also recommended to use the Prt starters to reduce bitterness in cheese. It was claimed thatthe rate of proteolysis in Cheddar cheese made using Prt- starters was similar to that in controlcheese. Lac- Lactococcus strains with high exopeptidase activity are commercially available ascheese additives. When inoculated into the cheese milk at 0.002%, individually or as a cocktail, theLac- cultures enhanced cheese flavor over that of the control. Assessment of proteolysis showedonly minor differences between the cheeses with respect to primary and secondary proteolysis butall adjunct-treated cheeses contained higher levels of amino acids than the controls throughoutripening.31.3.5 Use of high pressure treatmentUsing high pressure treatment (HPT) is one of the technological approaches for accelerated cheeseripening. HPT has emerged as a food processing technology primarily due to increasing interest innovel methods for preservation of foods. Applying high pressure to food products modifiesinteractions between individual components, influences rates of enzymatic reactions and caninactivate microorganism.In HPT, an increase in pressure tends to result in a decrease in volume, which enhances chemicalreactions, phase transitions and changes in molecular configurations. Irrespective of the size andgeometry, the pressure is instantaneously and uniformly distributed throughout the food. Theincreased pressure affects the environment of bacterial cell and many biochemical reactions incells. HPT can cause conformational change in protein but small macromolecules like amino acids,vitamins etc. are not affected.The application of HPT to cheese results in an increase in moisture content and pH and causechanges to the cheese matrix and lysis of cells, which contribute to ripening. HPT of cheese affectsthe pattern of proteolysis during ripening, the effect of which is dependent on the type of cheese,magnitude, duration and temperature of pressure treatment. The use of HPT appears to haveadvantages in both cheese manufacture and ripening. However, additional research is required todefine the operating conditions of HP treatment to provide positive effects in cheese making andripening.

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Module 16. Mechanized cheese making

Lesson 32MECHANIZATION AND AUTOMATION IN CHEESE MAKING32.1 IntroductionBefore starting discussion on mechanization and automation, it is a pre-requisite to understandthe basic difference between mechanization, automation and continuous production.Mechanization is a system in which almost all the stages are carried out by machinery instead ofmanually, as in the case of traditional practices. Automation is a mechanized system, which iscontrolled by an instrument fed by a programmer. Mechanization is a necessary precondition forautomation, but has different meaning. In a continuous system, raw materials are fed to themachine at one end and product comes out of the machine from the other end continuously. Incheese production, milk is fed to the machine at one end and it is continuously converted intocurd and cheese during passage through the machine.The pretreatments of milk for cheese making like standardization, bactofugation, pasteurization,etc. were already mechanized but with the developments taking place in the area ofmechanization and automation, now almost each and every stage of cheese manufacturing ismechanized. Steps like starter production, curd making, cutting, cheddaring, hooping, conveying,packaging, block forming, etc. have been mechanized for continuous and automated cheeseproduction. APV and Tetrapak are two of the leading industries which manufacture and supplymechanized systems of cheese production. Some of their machines are discussed in this chap ter.32.2 Cheese Vats: Double -O-vatTetra Damrow Double-O-Vat and Curd Master by APV.The Tetra Damrow Double-O-Vat 8 is specifically designed for the production of high qualitycheese curd and whey. The vat is suitable for the production of most cheese types like Cheddar,Emmental, Gouda, Blue, Feta as well as Pasta Filata. The design of the Tetra Damrow Double -OVat is based on the double circle principle, which ensures an optimum, efficient, yet carefultreatment of the cheese curd.Curd Master is another double O type vat fabricated by APV. It facilitates fast foamless filling,rapid mixing of all added components including rennet, gentle and precise cutting, fast wheydraw, controlled and fast heating and cooling, vertical vat with two outlets for fast emptying,efficient and gentle stirring. It is fully automated with touch screen and the vat can be cleaned bycleaning-in-place (CIP).32.3 Mould FillersTetra Tebel Casomatic is manufactured by TetraPak. It works in combination with two buffertanks. Each column is continuously fed by a pump with curd and whey mixture from a buffertank. The mixture is pumped to the top of the column. The curd settles under the level of whey.Via three perforated sections, whey is drained from the column. The speed of the whey drainage is125

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controlled by adjusting the drainage valves, depending on the pressure measured in thesesections. As the curd moves down inside the column, it is compressed progressively until a curdblock can be separated.32.4 Mechanised Cheddaring MachineThe Tetra Tebel Alfomatic is designed for continuous production of fused and stirred Cheddarand Pasta Filata cheese types. It is a totally enclosed machine, designed to automatically drain,acidify, texture, mill, salt and mellow cheese curd.The most common version of the machine is equipped with four conveyors mounted above eachother in a stainless steel frame. The cooked mass (curd/whey mixture) is uniformly distributed ona special drainage screen where most of the whey is removed. The curd is then passed through thefour conveyors one by one. The role of each of the conveyors isFirst conveyor---- it is equipped with stirrers to facilitate further whey removal.Second conveyor--- matting and fusing starts on this conveyor.Third conveyor---- the mat is inverted and cheddared. At the end of the conveyor, curd is milled.Fourth conveyor----salting takes place on this conveyor.

In the production of Mozzarella cheese, where salting is not required before stretching, a machinewith two or three conveyors is sufficient.

Fig. 32.2 Continuous Cheddaring machine with three conveyors suitable for Mozzarella cheese(Courtesy: Tetra Pak Processing Systems AB, Lund, Sweden)The other mechanized system for Cheddar cheese making is manufactured by APV. It has beengiven the trade name of Cheddar master. It is used for curd draining, cheddaring, milling, saltingand mellowing. It is available in the capacity ranging from 1000-9000 kg/h of cheese curd. APValso manufactures Mozzarella master for continuous production of Mozzarella cheese.32.5 Cooking And Stretching of Pasta Filata Types Of CheesePasta Filata (plastic curd) cheese is characterised by an elastic string curd obtained by cookingand stretching cheddared curd. The cheddared curd is worked in hot water at 82-85C until theyare smooth, elastic, and free from lumps. This step is necessary in order to develop elasticity incheese which is peculiar to such varieties. Continuous cooking and stretching machines are usedin large-scale production. The speed of the counter rotating augers is variable so that an optimalworking mode can be achieved. The temperature and level of cooking water are continuouslycontrolled. The cheddared curd is continuously transferred into the hopper or cyclone of themachine, depending on the method of feeding screw conveyor or blowing.

Fig. 32.3 Continuous Stretcher for Mozzarella cheese

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The systems discussed so far are mechanized systems for major steps in cheese making. Otherthan these systems, many other systems are also available like pre-press machines for pressing thecurd before cheddaring, final pressing to remove residual whey/moisture, mould emptier, rackfiller, rack brining system, rack unloader and rack washer. All these systems when installed inline, continuous and mechanized cheese making can be carried out. Processing lines fo r somevarieties of cheese will be discussed in the following sections.32.6 Continuous Cheddar Cheese makingStandardized and pasteurized milk is received in the vat where it is ripened, rennet is added toform curd, and curd is then cut and cooked. All these stages are completed in this vat. ThedoubleO-vats described earlier are mostly used to perform all these operations. The cooked curdand whey mixture is then pumped to cheddaring machine where dewheying, cheddaring, millingand salting take place. The curd is then fed to the block forming machine where the milled curdfuse together and blocks of uniform shape and size are formed. After this, the blocks are sealed byvacuum sealer, weighed, packed in cartons and kept for ripening. The process is sho wn in Fig.32.4.

Fig 32.4 Processing line for Cheddar cheese manufacturing

32.7 Continuous Gouda Cheese ManufacturingIn Gouda cheese making, the peculiar step is cooking the curd in whey through addition of about20% hot water. Before addition of water, about one third whey is drained. This process of heatingcurd with whey and hot water is called scalding. In mechanized system of Gouda cheesemanufacturing, the standardized milk is taken in the vat (1) and all other steps upto scalding arecarried out in this vat. After scalding, the content of the vat is transferred to a buffer tank (2) sothat the contents of more than one vat can be stored in the tank till further processing. This tank isequipped with agitators and is jacketed to supply chilled water in case activity of starterorganisms need to be curbed down. The curd is then pumped to the pre-pressing machine (3) likeCasomatic (TetraPak), where whey is removed and blocks of cheese are also formed. A fullymechanized system also comprises of: Mechanical lidding (4) of the moulds Transfer of moulds to conveyor or tunnel presses Filling and emptying of the presses Transport of moulds via a de-lidding station (6), a mould turning device (7), a mould emptying128

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system (8) and a weighing scale (9) to an advanced brining system (10).

Fig 32.5 Processing line for Gouda cheese manufacturing

Any variety of cheese production can be mechanized keeping in view the particular step thatdistinguishes one variety from other. For example, in the production of Mozzarella cheese, cheesecooker and stretcher are required which can be installed after Mozzarella cheddaring machine.

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